:es on Heating 
Ventilation 




Book . 



Copyright}!^. 



\^\\ 



COPYRIGHT DEPOSIT. 



NOTES 



ON 



HEATING and VENTILATION 



BY 



JOHN R. ALLEN 

W 

PROFESSOR MECHANICAL ENGINEERING 
University of Michigan 

Member American Society Heating and 
Ventilating Engineers 

Member American Society Mechanical 
Engineers 

Member American Society Promotion 
Engineering Education 



THIRD EDITION 



DOMESTIC ENGINEERING COMPANYI 

CHICAGO 

443 So. Dearborn Street 

1911 



^ 






A 



COPYRIGHT 
DOMESTIC ENGINEERING CO. 
1911 



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cP 



©aA^954G7 



TABLE OF CONTENTS. 

Introduction. 

Theory of heat and measurement of tempera- 
ture 1 

Chapter I. 

Heat losses from buildings and rules for deter- 
mining the heat-losses in different construc- 
tions 7 

Chapter II. 

Different forms of heating systems; their ad- 
vantages, disadvantages and relative economy. 28 

Chapter III. 

The design of a direct steam-heating system and 
the properties of steam; steam-tables; loss of 
heat from radiators; rules for direct heating.. 38 

Chapter IV. 

Design and installation of an indirect steam- 
heating system; rules for indirect heating.... 65 

Chapter V. 

Steam-boilers and steam-piping. Determination 
of size and details of construction 76 

Chapter VI. 

The connection of mains to risers and risers to 
radiators, with illustrations of different ar- 
rangements in practical use; steam-piping, 
piping systems, size of return-mains, valves 
and piping-connections 82 

Chapter VII. 

The design of a hot-water heating system; radi- 
ator heat-losses, rules for direct and indirect 
system 120 



Chapter VIII. 

Hot-water boilers and piping. Determination 
of size and details of construction 127 

Chapter IX. 

Ventilation and pollution of air by human be- 
ings, artificial lighting and chemical processes; 
systems of ventilation 141 

Chapter X. 

Design of hot-air heating systems, construction 
and rules 152 

Chapter XI. 

Fan system of heating, with tables of fan capac- 
ities and condensation in heater-coil; air-mix- 
ing systems 164 

Chapter XII. 

A central heating system; its design and instal- 
lation, with discussion of different methods 
of carrying pipes underground; specific ap- 
paratus; combination system of steam and hot 
water 187 

Chapter XIII. 

Pipe coverings, pipe, air-valves and fittings 209 

Chapter XIV. 

Auxiliary devices for heating systems, regula- 
tion of humidity and draft; air-washers and 
vacuum-heating systems 218 



SUBJECT INDEX 



Page 
A 

Air change, ordinary as- 
sumption for 146 

changes necessary 144 

dilution 143 

inlets and outlets 148 

mixing systems 182 

piping system 220 

pollution tests 142 

quantity to be supplied. 166 

valves 202, 212 

valves, pitch and sup- 
port of pipes 139 

washers 223 

Anchors and hangers 201 

B 

Boiler horse-pov/er 80 

Boilers 188 

fire tube 76 

hot-water 127 

proportion of 78 

steam 76 

water tube 76 

C 

Carbon dioxide 144 

Central heating systems.. 187 

Chemical processes 143 

Circuits, multiple and 

single 129 

Coils, heating 172 

Cold-air duct 155 

Combination of heating 

systems 36 

Combination system 87 

Combustion, products of.. 142 

Conduction 10 

Connections of radiators. 109 
Connection to mains and 

risers 99 

Convection 13 



Page 

Convection, losses, calcula- 
tion of 13 

Covering for pipes 209 

D 

Damper regulators 221 

Dams 83 

Determination of building 

heat-loss 21 

Direct and indirect com- 
binations 73 

Direct heating, rules for.. 55 
Direct hot- water heating. 32 

Direct steam-heating 32 

Disc fans 184 

Drainage, pipe 94 

Drip connections 101 

Duct, cold-air 155 

E 

Economy of different sys- 
tems 36 

Expansion joints 97 

Expansion of pipes 96 

Expansion tank 129 

F 

Factors for exposure 21 

Fan-heating systems ....164 
Pan, size, speed and 

horse-power 167 

Fan system of heating.... 34 

Fittings 217 

Fittings, resistance of.... 137 
Flow mains and risers. . . .128 

Flow, velocity of 186 

Flue proportion, hot-air. . .157 

radiators 50, 75 

Flues, foul air 157 

hot-air 156 

materials of 184 

Furnaces, hot-air 153 



HI 



Page 

Furnaces, hot-air, opera- 
tion of 159 



Grate surface, proportion 

of 79 

Grates 28 

Gravity system 90 

Gravity systems 189 

H 

Hangers and anchors 201 

Heat 1 

Heat generated by human 

beings 143 

Heat generated by illumi- 
nation 144 

Heat-loss for buildings 

determined 21 

Heat-loss from building. . 7 
Heat-loss from indirect 

steam radiators 65 

Heaters, cast-iron 176 

Heating and power sys- 
tem, combination of 191 

Heating apparatus, classi- 
fication of 28 

Heating systems, auxiliary 

devices for 218 

High -pressure systems. . . . 190 

Hot-air furnaces 30, 153 

furnaces, operation of. .159 

leaders and flues 156 

pipe, size of 73 

system 152 

system rules 160 

systems, proportions of. 158 
Hot-water boilers and 

piping 127 

direct 32 

heating indirect 34 

heating rules 124 

heating system 120 

piping 128 

Humidity regulations ....221 



Indirect heating rules.... 71 
hot-water heating 34 



Page 

hot- water radiators ....122 
radiators, heating effect 

of 70 

radiators, installation of 68 

steam heat losses 65 

steam-heating 33 

steam-heating design... 65 
Insulation 195 

J 

Joints, expansion 97 

L 

Leaders, hot-air 156 

Legs of the system 129 

Loss of heat from build- 
ings 14 

Low-pressure pump return 
system 191 

M 

Mains 82 

and risers, location of. . 99 

size of steam return... 91 

steam, rules for sizes of. 92 

Materials, specific heat in. 3 

Measurement of work 2 

Moisture -supply to heated 

air 154 

Multiple circuit system... 129 



One-pipe system 85 

Open and closed circuits. .134 
Overhead distribution.... 89 
Overhead system 132 



Paints for radiators, val- 
ues of 53 

Pipe 216 

and fittings, resistance 

of 137 

covering 209 

drainage 94 



IV 



Page 

expansion 96 

sizes 138, 199 

supports 119 

Pipes, method of cariy- 

ing 194 

Pipes, pitch and support. .139 

Piping, hot-water 128 

steam 82 

systems 84, 129 

Pitch 83, 129 

Power and heating sys- 
tems combined 191 

R 

Radiation 8 

Radiator connections . . . .109 

heat-losses 121 

installation 53 

sizes 47 

Radiators, different types 
of relative efficiency. . 44 

flue 50, 75 

heat loss under varying 

temperatures 51 

indirect hot-water 122 

loss of heat from 42 

Relation between heat and 

work 2 

Reliefs or drips 82 

Resistance of pipe and 

fittings 137 

Respiration, products of.. 142 

Return 82 

mains and risers 128 

mains, sizes of steam.. 91 

system, pump 191 

Risers 82 

Risers and mains, location 

of 99 

Rules for determining 
heat-losses 22 

S 

Single circuit system 131 

Single-pipe system 135 

Siphon 83 

Specific heat 3 

Steam and hot-water sys- 
tems combined 206 

heating direct 32 



Page 

indirect 33 

nature and properties of 38 

piping 82 

system indirect design.. 65 

Stoves 30 

Supporting of pipes 119 



Tables 

air dilution 143 

air-pollution tests 142 

capacity of mains 138 

capacity of risers 13t* 

condensation and heat 
given off by heater- 
coils 173 

condensation chart ....177 

conduction power 10 

dimensions and heat . 

losses 57 

disc-fan efficiency 183 

fan capacities 168 

fan efficiency 169 

fans, disc 184 

heat given off by illumi- 

nants 144 

heat-loss from flue radi- 
ators 50 

heat-losses from indi- 
rect radiators 67 

heat-transmission 52 

heat-transmission for 
varying pressures .... 211 

heater dimensions 176 

hot-air figuring 161 

indirect hot- water radi- 
ators 124 

indirect radiators — tem- 
peratures of leaving 

air 68 

loss from wrought iron- 
pipe and cast-iron 

radiators 42 

pipe-size practice 93 

pollution by lighting. .. .143 

properties of steam 40 

proportion of cast-iron 

hot-water boilers ....129 
proportions of hot-air 

heating systems 159 

pressure losses 181 



Page 

radiating power 9 

radiator tappings 54 

rate of transmission 121 

rating of house-heating 

boilers 80 

relative effectiveness of 
different thicknesses 

of covering 210 

relative size of steam 

and return main 94 

relative temperatures of 

air and room 63 

relative value of differ- 
ent pipe coverings. .. .210 
relative value of radia- 
tor paints 53 

results of computation, 

direct system 58 

results of computations, 

indirect system 72 

results of computations. 

direct hot- water 125 

size of hot-w^ater mains.137 
size of flues for indirect 

radiators 70 

specific heats 3 

specific heat of gases... 6 
speeds, capacities and 
horse-powers of single 
inlet, fans at various 

pressures 171 

steam 39 

temperature chart 178 

temperatures assumed in 

heating 25 

values of air-conditions. 17 

values of E 18 

values of K 20 

values of material and 
surface 18 



Page 

values of temperature 

difference 18 

velocity of hot-water 

circulation 137 

wrought iron and steel 
steam, gas and water 

pipe 215 

Tank, expansion 129 

Temperature 1 

Temperature regulation . . . 219 

Thermostat, Johnson 219 

Transmission of heat un- 
der various conditions.. 64 

Traps, steam 84 

Tunnels for steam sys- 
tems 197 

Two-pipe systems 86 

U 
Unit of heat 2 



V 



Vacuum heating systems. 225 

Valves 98, 217 

Valves, air 139 

Velocity of flow^ 13^ 

Ventilating ducts 177 

Ventilation 141 

Ventilation, effects of 

poor 147 

Ventilation systems 147 

W 

Water-hammer 83 

Water-line ... 83 

Water-seal 83 



VI 



PREFACE 

THE subject matter originally contained in this 
book was a reprint from a series of articles pub- 
lished in Domestic Engineering-. In this edi- 
tion the original text has been rewritten and a large 
amount of additional information included. 

This book wa-s written primarily to show that the 
subject of Heating and Ventilation could be developed 
in a logical way from the fundamental principles of en- 
gineering. The great lack has been in the amount 
of scientific information available regarding the actual 
laws of heat and the value of the constants entering 
into these laws. The University of Michigan has car- 
ried on, under the direction of ]\I. E. Cooley, Dean of 
the Engineering Department, a series of experiments 
for over twenty years. The results of these experi- 
ments are given in various tables and serve to give the 
designer data from actual experiments upon which he 
can base his calculations. 

There has been included in this edition a resume of 
the results of the German experiments and these meth- 
ods of determining lieat losses from buildings. This 
matter is largely reprints from a book published by 
the "Metal Worker" under the title, "Formulae and 
Tables for Heating'' by J. H. Kinealy. This book has 
been written primarily for the steamfitter and designer 
of heating systems. It presupposes some elementary 
knowledge of the details of construction and opera- 
tion of the sim])ler forms of heating plants. 

The author has used the previous editions as a text 
for his classes in Heating and Ventilation. The pres- 
ent edition has been written with a view to making 
the book more desirable as a college text. 

July 1, 1911. John R. Allen. 



INTRODUCTION 



Heat. — Heat is a form of motion. In modern sci- 
ence, all matter is conceived as being made up of 
small particles called molecules. These particles do 
not exist in a state of rest, but are in constant vibra- 
tion. If these particles move slowly the body is at a 
low temperature ; if they move more rapidly the body 
is at a higher temperature, the temperature of the 
body being determined by the rapidity of the motion 
of the particles. In measuring heat there are two 
properties to be considered — the intensity and the 
quantity. This may be compared to measuring water 
in a pipe. We measure the pressure of the water in 
the pipe by means of a gauge in pounds per square 
inch. The quantity of water is measured in pounds. 
In the same way the intensity of heat is measured by 
the thermometer in degrees and the quantity of heat is 
measured by comparison with the quantity of heat 
which a pound of water will absorb. 

Temperature. — Temperature, which is a measure of 
the intensity of the heat of a body, might also be con- 
sidered as measuring the velocity of the molecules of 
the body. In mechanical engineering all measure- 
ments of temperature are made on the Fahrenheit 
scale. On this scale the freezing point is taken at 32° 
and the boiling point as 212°, the tube of the ther- 
mometer between these points being divided into 180 
equal parts called degrees. 

We never know the total amount of heat in a body. 



Notes on Heating and Ventilation 

As it is impossible to bring any body to a condition 
of absolutely no heat, the heat in any body must al- 
ways be measured from some assumed zero point and 
in the Fahrenheit scale this assumed zero point is 32° 
below the freezing point. For theoretical purposes, 
however, it is highly desirable to have some absolute 
standard of heat. A perfect gas at 32° contracts about 
1/493 of its volume for each degree Fahrenheit that it 
is reduced in temperature. If, then, we keep on de- 
creasing the temperature of a perfect gas from 32°, 
until it reaches a point 493^ below 32° Fahrenheit, it 
would have, theoretically, no volume. If it has rro 
volume, the amount of heat which it contains must be 
zero. This point, then, is called the absolute zero. 
This point is manifestly an ideal one. To find the 
absolute temperature in degrees it is necessary to 
add to the Fahrenheit temperature 461 degrees, that 
is, 32° Fahrenheit corresponds to 493° absolute. 

Unit of Heat. — Heat is not a substance and it can 
not be measured as we would measure water in pounds 
or cubic feet, but it must be measured by the effect 
which it produces. Suppose it requires a certain 
amount of heat to raise a pound of water from 39° to 
40° Fahrenheit. It would require three times that 
quantity of heat to raise a pound of water from 39° to 
42.° Fahrenheit. The heat required to raise a pound 
of water one degree Fahrenheit is called a British 
thermal unit, and is designated by letters B. t. u. 

Relation Between Heat and Work. — Work is meas- 
ured in foot-pounds. The imit of work is the work 
required to raise one pound through a height of one 
foot. Ten units of work or ten foot-pounds would be 
the amount of work done in raising ten pounds one foot 
high or one pound ten feet high. Heat is a form of 
motion, hence there must be some definite relation be- 

2 



Notes on Heating and Ventilation 

tween heat and work. This relation was first deter- 
mined by Joule. By a series of experiments Joule found 
that one heat unit was equivalent to 778 foot-pounds. 
It is possible, then, to express heat either in heat units 
or in foot-pounds. 

Specific Heat. — Different substances require very 
different quantities of heat to produce the same change 
of temperature for the same weight. As for example, 
to raise one pound of water one degree requires one 
B. t. u. ; to raise one pound of ice one degree requires 
.504 B. t. u. ; to raise one pound of wrought iron one 
degree rcquires(^J^138 B. t. u. The heat necessary to 
raise one pound of a substance one degree, expressed 
in British thermal units, is called specific heat. The 
following table gives the specific heat of the principal 
substances which we meet with in engineering work: 

TABLE I. SPECIFIC HEATS. 
Substance. B. t. u. 

Liquids. 

Water 1.000 

Alcohol 622 

Turpentine 472 

Petroleum 434 

Olive Oil 309 

Metals. 

Cast iron , 1298 

Wrought iron 1138 

Soft steel 1165 

Copper 0951 

Brass 0939 

Tin 0569 

Lead 0314 

Aluminum 2185 

Minerals. 

Coal 2777 

Marble - 2159 

Chalk 2149 

Stones ffenerally 2100 

Limestone 2170 

Building Materials. 

Brick work 1950 

Masonry 2159 

Plaster 2000 

Pine wood 467 

Oak wood 670 

Birch 480 

Glass 1977 

3 



Notes on Heating and Ventilation 

Example. — It is required to raise the temperature of 
a cast iron radiator weighing 300 pounds from 70° to 
212°. The temperature through which the iron would 
.be raised would then be 212 minus 70° or 142°. From 
the table we see that it would require to raise one 
pound of cast iron one degree .1298 heat units, then to 
raise one pound 142° would require 142 times .1298 or 
18.43 heat units, and to raise 300 pounds one degree 
would require 300 times this amount or 5,529 B. t. 
u., the heat required to heat the radiator. This is 
important in heating as the walls of a cold building 
must be heated. 

Example.— A church 80'xl00' with walls 2y2 feet 
thick for 10 feet above the ground and for the re- 
maining 20 feet 2 feet thick. The roof has a ^ pitch 
and is made of 2"x8" rafters, 16 inches on centers, 
covered with 1 inch of pine boarding, tar paper and 
slate ^ inch thick. Main floor composed of two 1-inch 
thicknesses of boards laid on 2"xl2" joists, 16-inch 
centers. Ceiling is of plaster ^ in thick. The church 
has 20 windows, 6 feet wide and 15 feet high, 12 win- 
dows, 4 feet wide and 6 feet high, and 2 doors, 8 feet 
wide and 12 feet high. Allowing an addition of 15% 
of furnishings, find the heat required to raise the tem- 
perature of the church from 0° to 50°. 

Weight of stonework, stone weighing 160 pounds 
per cubic foot. 

370x10x2^x160=1,480,000 pounds 

268x20x2 xl60=2,350,000 
80 

— x40x2x2 xl60--=l,024,000 
2 



Total weight of masonry assuming I 
building to be without openings f *.»5)4,uuu 



Notes on Heating and Ventilation 

Weight of wood work. Weight per cubic foot taken as 40 
pounds. 
2x8 

x56. 2x75x2x40.= 37,600 pounds of rafters. 

144 
56.2x104x2x1/12x40= 39,000 pounds of roof boards. 

80x100x2x2/12x40=107,600 pounds of joists. 
2x12 

^x80x75x2x40...= 80,000 pounds of floor boards. 

144 

Total weight of wood- 
work 263,600 pounds. 

Slate — Weight per cubic foot taken as 170 pounds. 
56.5x104x2x1/48x170=41,600 pounds. 

Plaster — Weight per cubic foot taken as 90 pounds. 
(360x30x80x40^100x80) %xl/12x90=124,000 pounds. 

Air — Weight per cubic foot taken as .08 pounds. 

80 

(80x30x100-1 x40xl00) .08=32,000 pounds. 

Heat required. 2 

4,854,000x50x.2159=52,300,000 B. t. u. 

263,600x50x.65 = 8,580,000 B. t. u. 

41,600x50x.2159= 448,000 B. t. u. 

124,000x50x.2 = 1,240,000 B. t. u. 

32,000x50x.2375= 379,000 B. t. u. 

62,947,000 B. t. u. 

Adding 15% for furnishing = 9,440,000 B. t. u. 

Total to raise building and fur- 

nishing 50 degrees =72,389,000 B. t. u. 

This item is a large one in determining the size of 
the heating plant to be installed in a building inter- 
mittently heated. 

In solid substances the change in volume when they 
are heated is so small that it is not considered. In 
gases, however, the change in volume when the gas is 
heated without being confined, depends directly upon 
the absolute temperature and may be very large. 
When air is confined and is heated, it cannot expand ; 
if it does not expand there is no work done because, 
from our definition of work, it is necessary when work 
is done, that the body have some movement. On the 
other hand, when air receives heat and is free to ex- 
pand it does work. For instance, if air were confined 
in a cylinder by a piston, and this air were heated, the 
air would expand and the piston would be moved out. 

5 



Notes on Heating and Ventilation 

As the piston is moved through a certain space there 
must be work done. On the other hand, if the piston 
were blocked so that it could not move, then the air on 
being heated would do no work. Then in these two 
cases different amounts of heat will be required to 
raise the substance one degree, depending upon 
whether there is external work done or not. It is nec- 
essary then in gases that we consider two specific 
heats, the specific heat of constant volume and the spe- 
cific heat of constant pressure. For air the specific 
heat of constant volume is .1689, for constant pressure 
it is .2375. It is seldom that we use air in a confined 
space, so that, so far as this work is concerned, we 
shall in most cases consider the specific heat of air as 
.2375 — that is, to raise one pound of air one degree 
requires .2375 B. t' u., the pressure being constant. 

TABLE lA. SPECIFIC HEATS OF GASES. 

Constant Constant 

Substance. Pressure. Volume. 

Air .2375 .1689 

Oxygen 2175 .1550 

Hvdrogen 3.4090 2.4122 

Nitrogen 2438 .1727 

Steam 5000 .S500 

Carbonic Acid Co, 2479 .1758 

Ammonia 508 .299 



Notes on Heating and Ventilation 



CHAPTER 1 



Heat Loss from Buildings. — Heat is lost from a room 
in three ways — by the direct transmission of the heat 
through the walls and windows ; by the passage of air 
up the foul-air Hues, and„by the filtration of air through 
the walls and air leakage around doors and windows. 
The first two losses are easily determined, but the de- 
termination of the loss by filtration must always in- 
volve a large factor of judgment and experience. 

All building construction is more or less porous. 
This is well exemplified by the old experiment made 
with a common brick. Two cornucopias of paper are 
pasted on opposite sides of a common brick, the larg« 
end of the cornucopias being fastened to the brick. Op- 
posite the small end of the cornucopia at one side is 
placed a lighted candle. By blowing into the cornucopia 
on the opposite side, the candle may be blown out, the 
air having passed directly through the brick. 

The experiments which have been made in order to 
determine the loss generally tend to show that in the 
ordinary well-constructed building the air in the room 
will change about once per hour, when all doors and 
windows are closed. 

In order to study the other heat losses from a room 
it will be necessary to study the laws of cooling. A 
body may be cooled in three different ways — by radia- 
tion, by conduction and by convection (contact of 



Notes 



o n 



Heating and Ventilation 



air). In order to understand these losses more thor- 
oughly, each will be considered separately. 

Radiation. — The heat that passes from a body by 
radiation may be considered similar to the light which 
is given off by a lamp. There is always a transfer of 
radiant heat from the body of a higher temperature to 
the body of lower temperature. The amount of heat 




Fig. 1. 

radiated will depend upon the difference in tempera- 
ture between the bodies and the substance through 
which this heat passes and the material composing the 
surface from which the heat is radiated. 

The losses by radiation may be better understood by 
referring to Fig. 1. Suppose the plate PP to be of 

8 



Notes on Heating and Ventilation 

cast iron 1 foot square and 1 inch thick. Let us sup- 
pose this plate to be on both sides at a temperature 
of 60°. Let this plate form one side of a room, the 
walls WWW being non-conducting substances and at 
a temperature of 59°, the air in this space being at a 
temperature of 60°. Since the plate and the air in 
the space are at the same temperature, there will be 
no loss of heat from the air to the walls, but all the 
heat that passes from the plate PP to the walls must 
pass by radiation. For ordinary temperatures of heat- 
ing surfaces, say 60 or 70°, the loss by radiation will 
equal the difference in temperature between the hot 
body and the cold body multiplied by a factor repre- 
senting the radiating power of the body. The follow- 
ing table gives the radiating power of different sub- 
stances : 

TABLE IT. RADIATING POWER. 

Radiating power of bodies, expressed in heat units, given off per 
square foot per hour for a difference of one degree Fahrenheit. 
(Peclet.) 

Copper, polished 0327 

Iron, sheet 0920 

Glass 595 

Cast iron, rusted 648 

Building stone, plaster, wood, brick 7358 

Woolen stuffs, any color 7522 

Water 1.085 

Heat is radiated in straight lines exactly as light is 
given off from the source of light. We may have heat 
shadows the same as we have light shadows and the 
intensity of the heat is inversely proportional to the 
square of the distance from the source. Some bodies 
are transparent to heat and other bodies absorb heat, 
the same as some bodies are transparent to light and 
others absorb light. The transparency of bodies to 
heat is called diathermancy. Gases, such as air, oxy- 
gen, nitrogen, and hydrogen, are almost perfectly 

9 



Notes on Heating and Ventilation 

transparent to heat, while wood, hair, felt and other 
non-conducting bodies are almost perfectly opaque to 
the transmission of heat. The loss of heat by radia- 
tion is independent of the form of a body so long as it 
does not radiate heat to itself. The color or condition 
of the surface of different bodies affects their radiant 
power. Smoothly polished surfaces radiate less heat 
than rough surfaces. As, for instance, a surface painted 
with lamp black will radiate over 13 times as much 
heat as a polished copper surface. 

Example. — Suppose we have a glass surface five 
square feet in area. The glass surface is at a tempera- 
ture of 70° and the objects surrounding it are at a 
temperature of zero. From the table we see that one 
square foot of glass (surface) loses .595 heat units in 
an hour for a difference of one degree between it and 
the surrounding objects. For a difference of 70°, then, 
each square foot of glass would lose 70 times that 
amount, or 41.5 heat units, and 5 square feet of glass 
would lose 5 times that amount, or 207.5 heat units per 
hour by radiation only. 

Conduction. — The heat transmitted by conduction is 
the heat which is transmitted through the body itself. 

TABLE III. CONDUCTING POWER. 

The conducting power of materials, expres.sed in the quantity of 
heat units transmitted per square foot per hour by a plate one 
Inch thick, the surfaces on the two sides of the plate differing in 
temperature by one degree. (Peclet.) 

B. t. u. 

Copper 515 

Iron 233 

Lead 113 

Stone 16.7 

Glass 6.6 

Brick work 5.6 

Plaster 3.7 

Pine wood -76 

Sheep's wool .323 

10 



Notes 



o n 



Heating and Ventilation 



For example, take the condition shown in Fig. 2. PP 
is a plate, one side of which is enclosed by the walls 
WW. Let the temperature of the plate outside be 59°, 
the temperature on the inside of the plate be 60° ; the 
temperature of the walls be 60°, and the temperature 
of the air in the room be 60°. Then all the heat that 



'///////////A 




\N60 



I 



Air 60' 



I 



vt i 

i 
i 



\N60 



I 






Fig. 2. 

is lost by the room must be lost by direct conduction 
through the plate PP. The amount of heat conducted 
will depend upon the material of which the conductor 
is composed and in addition it will also depend upon 
the difference in temperature between the two sides of 
the plate and upon the thickness of the plate. The 



11 



Notes 



o n 



Heating and Ventilation 



conduction through any plate may be calculated as fol- 
lows: 

Multiply the factor given in Table III by the 
difference in temperature between the two sides of the 
plate and divide the result by the thickness of the plate 
in inches. The quotient will be the heat transmitted" 
by conduction per square foot of surface. 




V^ 60 






Air 59 



4 

60"$ 



\N60' 



J 






"^mmmmmmmmm^A 



Fig. 3. 

Example. — Suppose a boiler plate 5 feet square, Vi- 
inch thick, to have a temperature of 70° on one side 
and a temperature on the opposite of 200°. The dif- 
ference in temperature of the two sides of the plate 
would be 130°. The amount of heat conducted would 
then be 233 X 130 ^ >^ = 15,145 B. t. u. per square 



12 



Notes on Heating and Ventilation 

foot of plate per hour. Then five square feet would 
transmit five times this amount, or 75,725 B. t. u. in 
one hour. 

Convection. — Loss by convection is sometimes 
termed loss by contact of air. Take, for example, the 
condition shown in Fig. 3. Let P be a vertical plane 
of metal one foot square, having its surfaces main- 
tained at 60° temperature. Let the walls WW also be 
at a temperature of 60°. Let the air in the room be 
59°. In this case there will be no loss of heat from 
the walls to the plate by radiation and there will be 
no loss through the plate by conduction, but heat will 
be transmitted from the walls and the plate to the air 
of the room. The air which comes in contact with the 
warmer walls will be heated. As air is heated it be- 
comes lighter and rises and a current is formed. This 
produces a circulation of air, and this circulation of 
air gives rise to a loss of heat by convection or contact 
of air. 

The loss of heat by convection is independent of the 
nature of the surface, wood, stone or iron losing the 
same quantity of heat, but it is affected by the form of 
the body — that is, a cylinder and a sphere would lose 
different amounts of heat per square foot. Take the 
steam radiator, for example. The air nearest the radi- 
ator becomes heated and rises ; as it rises its place is 
taken by other colder air coming off the floor so that 
a current of air is established. In the ordinary type 
of radiator, the loss by contact of air represents about 
half the loss of heat, the balance being loss by radia- 
tion. 

Calculation of Convection Losses. — The calculation 
of the heat lost by convection is quite complicated and 

13 



Notes on Heating and Ventilation 

different expressions have been derived for this loss for 
different forms of surfaces. Those developed by Peclet 
are given in Box's treatise on Heat. 

The rules given for convection in the text-books on 
heat cannot, as a rule, be applied to the loss of heat 
from buildings. All these rules assume that the air 
surrounding the object is in a perfectly quiescent state. 
In buildings this is not the case, for the air surround- 
ing a building is rapidly circulated by the winds. The- 
oretically a high building would lose proportionally 
less heat than a low building, because in the upper 
stories there would be a smaller difference in temper- 
ature between the air inside the room and the air out- 
side than in the lower stories. This, however, is not 
the case, as the wind circulates the air outside the 
building and makes the temperature of the air sur- 
rounding the building on the outside practically the 
same at all levels. 

Inside the room, however, the air at the top of the 
room is much warmer than that at the floor. The re- 
sult is that the rate of transmission of heat in rooms 
with high ceilings is appreciabty higher than in rooms 
with low ceilings, as in the room with a high ceiling 
we have a greater difference of temperature between 
the inside and the outside air at the ceiling. This dif- 
ference is not ordinarily considered unless the height 
of the room exceeds ten feet. If the height of the room 
does not exceed ten feet the temperature taken five 
feet above the floor line may be assumed as the average 
temperature of the room. 

The loss of heat from buildings was first investi- 
gated both experimentally and theoretically by Peclet. 
The greater part of his work is given in Box's treatise 

14 



Notes on Heating and Ventilation 

on Heat. The results obtained by Peclet are difficult 
to apply practically and nearly all the rules that are 
used to determine the loss of heat from a building are 
largely empirical. The constants determined by the 
German government are probably the most reliable 
we have. 

The German formulas and tables w^ere translated by 
J. H. Kinealy and published under the title "Formu- 
las and Tables for Heating," by the "Metal Worker." 
The following pages outline the German method as 
given in the pamphlet mentioned. 

In the simplest form of building the walls consist 
of one solid piece of the same material and in this 
case the transmission of heat is from the air of the 
room to the wall by convection, through the wall by 
conduction and from the surface of the wall to the cold 
air outside by convection. Such a wall is shown in 
Fig. 4. 

A solid wall may be ^made up of a series of layers 
of different materials, as shown in Fig. 5. The trans- 
mission of heat, however, goes on in the same way. 

In a wall such as is shown in Fig. 6, the heat passes 
through each of the consecutive w^alls just as it does 
through a solid wall. Heat always passes from a 
warmer to a colder body. Hence t/, the temperature 
of the inside of the wall, must be less than the tem- 
perature of the room t, and the temperature to' must 
be greater than the temperature of the outside of the 
wall to'. Each particle in a section of the wall must 
have a different temperature, the temperature dimin- 
ishing as the particle is nearer and nearer to the out- 
side wall. 

The quantity of heat transmitted through a given 
area of wall must be the same for each point in the sec- 

15 



Notes on Heating and Ventilation 

tion when the wall has once reached a stable condition. 
The quantity of heat which passes per hour from the 
warm air of the room to a square foot of wall will be 
in Figs. 4, 5 and 6 a^ (t^ — t^'), and the heat which 
passes from the outside wall to the cold outside air is 
^0 (to' — to). If the wall has an air space as in Fig. 6, 
the heat Avhich passes to the air space will be a/(t2' — 




- r„ 




"1^ 



J' 



f/6 5 




ta), and the heat given by the air space to the outer 
wall will be a/(t2— t/')- 
The heat that passes through the wall by conduc- 

tion; as stated before, will be in Fig. 4 — (t^' — t^,'), 
and in Fig. 6 for the inner wall — ^ (t^' — tg')? and for 



Xi 



62 



the outer wall — (tj" — to'). If the layers of this wall 

^reof similar material, e^ and eo will be equal. 

In order to use these expressions it is necessary to 
know the temperature of the wall surface. These tem- 
peratures are not known. The only known temperatures 
are the temperature of the air inside the room and the 
air outside the building. Let us assume that the heat 



16 



Notes on Heating and Ventilation 

transmission through the wall may be represented by 
the expression k (t^ — t^), where k is a constant to be 
determined. 

The amount of heat passing through the wall at 
each point is constant, hence we have for Fig. 4: 

K (ti— to)-ai(t,— t/)=a,(t,/— t„) = — (ti'— to') (1) 

X 

and for Fig. 6 : 

K (ti— to)=a,(ti— ti')=a,'(t,'— t,)=a,'(t2— t2")=a,(t/— to) 
ei 62 

=— (ti'— 12')=— (ta"— to') (2) 

Xl X2 

Solving for k in equation (1) 

K = (3) 

1 1 X 

— + — + — 
ai ao e , 

and in equation (2) 

K = (4) 

11 1 1 X, X2 

ai a/ a2' ao ei 62 

For thin glass or thin metal walls, — is a very small 
quantity and may be neglected. 

The values of a and e must be known before k can 
be determined. The value of the convection factor, 
a, is determined by Grashof by the following equation: 

(40 c + 30d) T 

a = c -!- d H 

10,000 

c as a factor depends on the condition of the air, 
whether at rest or in motion. Rietschel gives the fol- 
lowing values for c : 

TABLE IV. VALUES OF c. 

e. 

Air at rest, air in rooms 82 

Air with slow motion, air in rooms in contact with windows.. 1.03 
Air with quick motion, air outside of a building 1.23 

17 



Notes 



o n 



Heating and Ventilation 



d is a factor depending upon the material compos- 
ing- the wall and on the condition of the surface. The 
values for d ma}^ be taken as follows : 



Substance. 

Brickwork 74 

Mortar and similar materials .74 

Wood 74 

Glass 60 

Cast iron 65 

Paper 78 



TABLE V. VALUES OF d. 
d. Substance. 



d. 



Sheet iron 57 

Sheet iron polished 092 

Brass polished 053 

Copper 033 

Tin 045 

Zinc 049 



T is the difference between the temperature of air 
and that of the surface of the wall. For poor con- 
ductors or very thick walls it mav be taken as zero. 





riGj 

In approximate calculations it is usually taken as 
zero. The following values of T are given by Rietschel : 

TABLE VI. VALUES OF T. 

Brick work 5 inches thick 14.4 

Brick work 10 inches thick 12.6 

Brick work 15 inches thick 10. 8 

Brick work 20 inches thick 9.0 

Brick work 25 inches thick 7.2 

Brick work 30 inches thick 5.4 

Brick work 40 inches thick 1.8 

For single windows 36. 

For double windov/s 18. 

For wooden doors 1.8 

Table VII gives values of e. These values vary 
considerably for different authors. 

TABLE ^ai. VALUES FOR e. 

e. 

Brick work 5.6 

Mortar, plaster 5.6 

Rubble masonry 14. 



18 



Notes on Heating and Ventilation 

Limestone 15. 

Marble, fine grained 28. 

Marble, coarse grained 22. 

Oak across the grain 1.71 

Pine, with the grain 1.4 

Pine, across the grain .76 

Sandstone 10. 

Glass 6.8 

Paper 27 

For example, assume a brick wall as shown in Fig- 
ure 7. Tliere are four air contact surfaces and two 
walls through which conduction takes place, then : 

K is the same as in equation 4. 

Rietschel assumes a/, a/' and ao' equal and he uses 
the same value of T as for a solid of thickness equal 
to the brick work without the air space. 

(40X.82+30X.74)10 

a^ = a,'=a/=.82+.74H =1.62 

10,000 
(40X1.23+30X74)10 

a,— 1.23+.74H =2.04 

10,000 
Since both walls are of brick work 
Xi 4.75 

Ci 5.6 
X, 8.25 

= =1.47 

e 5.6 

Substituting in equation (5) 

1 

k = =.214 

.62+.62+.624-.49+.85-J-1.47 
Making this same calculation, neglecting T gives 

k=.210 

19 



Notes on Heating and Ventilation 

The following- values of k have been determined by 
using equations (3) and (4) as shown in the example. 

TABLE VIII. VALUES OF k ADOPTED BY PRUSSIA. 



Inches thick 492 

thick 348 

thick 266 

thick 226 



Brick 


. work. 


4.72 


inches 


9.85 


inches 


15 


inches 


20.1 


inches 


25.2 


inches 


30.2 


inches 


35 


inches 


40.5 


inches 


45.6 


inches 



thick, 
thick, 
ihick, 
thick, 
thick. 



.184 
,164 
.133 
.123 
.113 



Masonry, sandstone. k. 

11.8 inches thick 451 

15.7 inches thick 39 

19.7 inches thick 348 

23.8 inches thick 318 

27.6 inches thick 287 

31.6 inches thick 266 

35.4 inches thiclc 246 

39.4 inches thick 226 

43.3 inches thick 205 

47.2 inches thick 195 



For limestone masonry the values of k should be 
taken 10% larger than those given for sandstone. 



TABLE IX. 

Values of k for various forms of brick walls. 
81/4x4x2, laid with %-inch mortar joints, 
thick 



Brick are assumed 
Plastering % of an inch 







Outside Walls. 


Inside Walls. 










Plaster 










One Side 


Board 










Plastered 


and Air 


Plas- 








and 2.4 Air 


Space Be- 


tered 


Thickness 


No 


One Side 


Spaces in 


tween Wall 


Both 


of Wall. 


Plaster. 


Plastered. 


the Wall. 


and Board. 


Sides. 




k 


k 


k 


k 


k 


% brick 


.52 


.49 


, , 


.29 


.43 


1 


.37 


.36 


.25 


.24 


.33 


1% " 


.29 


.28 


.21 


.21 


.26 


2 


.25 


.24 


.19 


.20 




2% " 


.22 


.21 


.16 






3 


. .19 


.18 


.14 






3^ " 


.16 


.16 


.13 






4 


.14 


.14 


.12 






41/^ " 


.12 


.12 


.. 







For doors, wooden walls and windows, the values of 
k are given in Tables X, XI and XII. 



TABLE X. DOOR OR WOODEN WALLS. 



Thickness — 



Pine 



Inside, 
k 

inch 52 

inch 44 

inch 39 

inch 34 

l^ inch 31 

2 inch 26 



V2 
% 

1 

11/4 



Outside, 
k 
.56 
.47 
.41 
.36 
.32 
.27 



Inside, 
k 
.64 
.59 
.54 
.50 
.47 
.41 



Oak 



Outside, 
k 

.70 
.63 
.58 
.54 
.50 
.43 



TABLE XI. WINDOWS' AND WALLS. 

Single window 1.03 

Single window, double glass 62 

Double window 46 



20 



Notes on Heating and Ventilation 

Single skylight 1.16 

Double skylight 48 

Stud partition, lath and plaster one side 60 

Stud partition, lath and plaster both sides 34 

Lath and plaster ceiling space above unheated 62 

Floor % inch thick, cold space below 45 

Floor % inch thick, lath and plaster on under side, cold space 

below 26 

Floor double 1% inches thick, cold space below 31 

Floor double 1*/^ inches thick, lath and plaster on under side, 

cold space below 18 

TABLE XII. OUTSIDE WALLS. 
Walls having lath and plaster on the inside, and outside is covered 
as described. 
Outside covering — k: 

Overlapping clapboard 7-16 inch thick 44 

Paper and clapboards 31 

% inch sheathing and clapboards 28 

% inch sheathing, paper and clapboards 25 

Factors for Exposure.— -The heat losses given in the 
tables should be increased as follows : Where the 
room has a north or northwestern exposure and the 
winds are severe, add 20 to 30 per cent. When the 
building is heated in the day time only and allowed 
to cool during the night, add 20 per cent. When the 
building is heated occasionally — for example, a 
church — add from 40 to 50 per cent. Where a room 
has a northerly exposure and is subjected to extremely 
high winds, add 30 per cent. It is usually advisable 
to assume for unwarmed spaces, such as cellars and 
attics, a temperature of about 32°. For vestibules and 
entrances unheated, which are being frequently opened 
to the outer air, a temperature of 20° may be assumed. 

Determination of the Loss of Heat from a Build- 
ing. — In determining the loss of heat from a building 
all surfaces should be considered which have on the 
outside a lower temperature than the temperature in 
the room.' If a room is situated over a portion of the 
cellar which is not heated, the loss of heat through 
the floor should be considered. If the room has over 
it an unheated ^ttig the loss through the ceiling should 

91 



Notes on Heating and Ventilation 

be considered. In most cases where the attic has no 
window it is warm enough so that the heat loss 
through the ceiling may be neglected. The loss 
through the sides of a room which is surrounded by 
rooms at the same temperature may be neglected. 
Doors entering directly into a room from outside are 
roughly considered to lose the same amount of heat per 
square foot as windows. 

Rules for Determining the Loss of Heat. — A com- 
mon rule for the loss of heat from a building is that 
given by Professor R. C. Carpenter in his book on 
"Heating and Ventilation." This rule is developed 
from the following consideration : Referring to Table 
IV, we notice that one square foot of glass conducts 
approximately four times as much heat as a brick 
wall 20 inches thick. If, then, we divide the wall sur- 
face by 4, the result will give us the number of square 
feet of glass surface, which would lose the same quan- 
tity of heat. Adding to this the actual glass surface 
would give us the total equivalent glass surface. In 
addition to this heat transmitted through the walls we 
must add the heat which is lost by the air which 
passes directly through the walls themselves. It is 
assumed that for ordinary sized rooms the air in the 
room will be changed about once an hour, so that 
we must figure on heating the entire air in the room 
about once per hour. One cubic foot of air weighs, 
approximately, 1/13 of a pound. To raise a pound 
of air one degree requires .238 B. t. u. Then to 
raise one cubic foot of air one degree would require 
.238 X 1/13 = .0183 B. t. u. or one heat unit will heat 
1~.0183=54.6 cubic feet, or in round numbers say 55. 
If, then, we divide the contents of a room by 55 we 

22 



Notes on Heating and Ventilation 

will have the heat lost by filtration through the walls. 
Adding these factors together will give the total heat 
lost from the room. This rule may be expressed more 
concisely as follows: 

Rule 1. — Divide the contents of the room by 55 ; add 
the glass surface and add to this sum the zvall surface di- 
I'ided by 4. The sum zmll be the heap lost from the room 
per degree difference of temperature between the air in 
the room and the air outside the room. Multiply this 
sum by the difference in temperature betzveen the air in- 
side the room and that outside of Vhe room and the 
product zvill be the heat lost from the room. 

This rule can be expressed algebraically as follows : 
Let^ C represent the volume of the room, W the zvall 
surface, G the glass surface and d the difference of tem- 
perature between the air outside and the air inside the 
room. The heat loss from the room per hour expressed 

Cn W 

1 \- G y d, zvhere n 

55 4 

is a factor which depends upon the tightness of the room 
and varies in value from 1 — 3. For ordinary room n=l, 
for corridors 1.5, for vestibules 2 Po 3. 

It is quite customary to assume the difference in 
temperature between the air in a room and the air 
outside to be 70°. Where the windows are poorly 
fitted or the house loosely built the loss by filtration 
should be doubled, and in halls where the doors are 
being opened and closed frequently this should be 
multiplied by three. 

There is one criticism on this method of figuring 
the heat loss in the room. The diffusion loss is as- 
sumed to depend upon the cubic contents of the room. 

23 



/';/ B. t. u.'s zi'ould be 



Notes on Heating and Ventilation 

This of course is manifestly not correct, as the diffu- 
sion loss occurs through the walls and windows and 
must depend upon the area of the walls and windows. 
The rule, however, will work very well for rooms of 
average size, but where the rooms have excessive wall 
and window surfaces, or where the cubic contents of 
the room is large compared to the wall and window 
surfaces, this rule will give inconsistent results. The 
following rule seems to the author to be capable of a 
much wider application : 

Rule 2. — Divide the wall surface by 4; add the glass 
surface; mnlPiply this sum bv the difference in tempera- 
ture betzveen the air in the room and the air outside, and 
then multiply the result by ly^. This rule is for a well 
constructed building. If the building is old and poorly 
built then instead of multiplying by 1^^ t^he result should 
be multiplied by 2;- entrance halls multiplied by 2^. 
This rule may be expressed algebraically as follows : 
Let W represent the wall surface, G the glass surface, 
and d the difference of temperature between the air out- 
side and the air inside the room. Then the heat loss 
from the room per hour expressed in B. t. u.'s would 

\ w \ 

be < h G Yd n, where n is a factor which depends 

upon the construction of the house or location of the 
room and varies in value from 1.5 to 2.5, as stated above. 
In figuring the radiating surface for any room the 
cubic contents should always be taken into consideration. 
In a large room with a small exposed wall surface, if 
only enough radiation is put in to cover the loss from 
walls and windows, the room will be slow to heat. In 
^(j^ition to taking care of the loss from walls and vyiri- 

84 



Notes on Heating and Ventilation 

dows it is necessary for the radiator to heat the air in 
the room itself. In order to do this a large proportion 
of this air must either pass through the heating device 
or be carried out by the ventilating flues, so that where 
the cubic contents of a room is large it is advisable to 
add from 10 to 20 per cent to the radiating surface to 
allow for the heating of the air in the room itself. The 
above remark applies only when the building is inter- 
mittently heated ; when the building is continuously 
heated it is not necessary to consider the volume of the 
room. 

The following temperatures are usually assumed in 
determining the heat losses : 

TABLE XIII. TEMPERATURES ASSUMED IN HEATING. 

Degrees. 

Temperature of stores 68 

Temperature of residences 70 

Temperature of halls and auditoriums 64 

Temperature of prisons 65 

Temperature of factories 60 to 68 

Temperature of cellars not warmed 32 

Temperature of outside entrances 20 

Temperature of attics not warmed 32 



^^ 



The average temperature for the period of the year 
during which buildings are heated throughout the Cen- 
States may be assumed to be approximately 35°. 

The following examples will show the method to be l^ - 
pursued in determining the heat lost from a building: 

Example 1. — Suppose a room, as shown in Fig. 
8. Let the temperature be maintained in the room at 
70 degrees, the temperature of the outside air be 0. Let 
the walls be of brick, 8 inches thick, plastered on plaster 
board on the inside, the windows be 2)4x6 feet, the ceil- 
ing of the room be 10 feet high. Let the room be on 
the second floor of the building, the rooms above and 
b^low heated- The window surfaces are 22x2^2x6=30 

25 



Notes 



o n 



Heating and Ventilation 



square feet. The total wall surface is 20x10=200 square 
feet. The net wall surface is 200 — 30^170 square teet. 
Then the lieat lost from the room per degree difference 




Fig. 8. 

of temperature by rule 2 would be lT0^4-|-30=:72>4. 
As the difiference between the outside and inside tem- 
perature is 70°, the total heat lost is 72>^x70=5,07o 
B. t. u. per hour. 

26 



Notes on Heating and Ventilation 

Example 2. — Take the same room as Example 1, 
except that the room is covered by a flat tin roof. 
The air space between the ceiling of the room and 
roof should be assumed to be at a temperature of 32°. 
Then, in addition to the loss figured in Example 1, 
there will have to be added the loss due to the tin 
roof. The area of the ceiling of the room would be 
14x20=280 square feet. Referring to Table IV we 
find the loss per hour through ceilings of plaster con- 
struction to be .62 B. t. u. per degree difference of 
temperature; then the loss through this ceiling would 
be, per degree of temperature, .62X280=173.0 B. t 
u. The room being at 70° and the attic space 32°, 
the difference in temperature would be 70 — 32=38 
degrees. The total loss through the ceiling would 
then be 29.1X38=6,574 B. t. u. Adding this to the 
loss found in Example 1 we have a total loss from the 
room, 5,070+6,574=11,649 B. t. u. 

A more accurate method is to figure the actual loss 
through the walls and windows from the constants 
in tables IX and X. 

The loss from walls (.24X170) 70= 2,856 

The loss from windows (1.03X30) 70= 2,163 



Total loss from walls and windows= 5,019 

To allow for diffusion this sum must be multiplied 
by Ij/, making a gross loss of 7,528. 



27 



CHAPTER II. 

DIFFERENT FORMS OF HEATING. 

Classification of Heating Apparatus. — The different 
heating systems may be classed under two general 
heads — Direct and Indirect. In direct heating the 
heating surfaces are placed in the rooms to be heated, 
as, for instance, stoves, steam radiators or hot water 
radiators. In indirect heating systems the heating 
apparatus is placed in some other room and the heat 
carried to the room to be heated by means of pipes. 
Under this head would be included hot air furnaces 
and the various systems of heating in which fresh 
cold air is made to pass over steam or hot water radi- 
ators on its way to the room. 

The indirect systems of heating naturally divide 
themselves into two other classes, those using natural 
draft and those using forced draft. A good example 
of natural draft indirect heating is the hot air furnace, 
where the circulation of air through the house is pro- 
duced by the difference in temperature between the 
air in the hot air flues and the cold air outside the 
flues. The fan system of heating, used in heating 
school buildings and churches, are good examples of 
the forced draft system. In this case the draft is 
largely produced by mechanical means, usually a 
disc fan or a pressure blower. 

In order to understand better a discussion of the 
various forms of heating which will come later, it is 
desirable to understand in general the advantages and 
disadvantages of the various forms of heating. 

Grates. — The most primitive form of heating ap- 



Notes on Heating and Ventilation 

paratus is the grate. In the grate the air which passes 
through the fire and is heated by the fire all passes up the 
chimney and only the heat given ofif by radiation to the 
walls and objects in the room is effective in heating the 
room. In grates of better construction this is somewhat 
improved by surrounding the grate by fire brick so 
arranged that the brick will become highly heated and 
radiate heat to the room. But the fact that all the 
air heated by the grate passes up the stack makes 
this a very uneconomical form of heating. In the 
best form of open grates only about 20 per cent of 
the heat of the fuel is effective in heating the room. 
This form of heating, however, has been defended by 
many. It is a very popular form of heating through- 
out England and Scotland. The feeling of a grate- 
heated room is quite different from that of a room 
heated by other systems. All the heat is given off 
by radiation and the air in a grate-heated room is at 
a considerably lower temperature than the objects and 
persons in the room, owing to the fact that radiated 
heat does not heat the air through which it passes. 
The air of the room being at a lower temperature, 
its capacity for moisture is not increased as much 
as it would be were the air heated to a higher tem- 
perature. The result is that the air contains propor- 
tionally more moisture than is the case in other forms 
of heating. This, no doubt, is an advantage. On the 
other hand, it is impossible to heat the room uni- 
formly, and a person is hot or cold, depending upon 
his distance from the grate. Heating by means of 
grates is practiced only in the more moderate climates. 
The grate is useful in the houses heated by other 
forms of heating, as it serves as a most efficient foul 

29 



Notes on Heating and Ventilation 

air flue. The introduction of a large number of grates 
into a house adds materially to the ease with which 
the house may be ventilated. 

Stoves. — The stove is a marked improvement over 
the grate as a form of heating, particularly from the 
standpoint of economy. The modern base burner 
stove is one of the most economic and efficient forms 
of heating, making use of from 70 to 80 per cent of 
the heat in the fuel. In heating by a stove the heat 
is given off both by radiation and by convection. The 
hot surface of the stove being at a higher tempera- 
ture than the surrounding objects in the room, radiates 
its heat directly to these objects. In addition the 
air surrounding the stove is heated and rises, passing 
along the ceiling to the cold wall and window sur- 
faces where it is cooled, drops to the floor and passes 
along the floor back to the stove to be again heated. 
In selecting a stove to heat a given room care should 
be taken to select one of ample size so that only in 
the coldest weather would it be necessary to crowd 
it; that is, keep on the drafts in order to heat the 
room. At the present time the stove as a general 
source of heat is being rapidly discarded because of 
the attendance required, the space occupied and the 
itnsightly appearance of the stove. Another serious ob- 
jection to the stove is the fact that it does not furnish 
ventilation to the room which it heats. 

Hot Air Furnaces. — The hot air furnace is a natural 
outgrowth of the stove. In this system one large 
stove is placed in the basement of the building, the 
air is taken from the outside, passed over the sur- 
faces of the stove or furnace, carried up through the 
flues to the rooms to be heated. The principal ad- 

30 



Notes on Heating and Ventilation 

vantage of the hot air furnace is that it provides a 
cheap method of furnishing both heat and ventilation, 
it requires little attendance and does not deteriorate 
rapidly when properly taken care of. The greatest 
disadvantage of this system is in the fact that the 
circulation of the heated air depends entirely upon 
natural draft ; that is, it depends upon the difference 
in weight between the air inside the flue and the air 
outside the flues. This difiference of weight is ex- 
tremely small, so that the force producing circulation 
in the flue is always small. This force is easily over- 
come either by the winds or by the resistance of the 
piping. When a very strong wind blows against one 
side of the house it is difficult to heat the rooms on 
that side of the. house. If the system is carefully de- 
signed, however, this difficulty can be overcome in 
a measure. Another serious objection to the hot air 
furnace is that it is seldom dust tight and dust and 
ashes are carried into the room. In general, how- 
ever, the hot air furnace may be considered as a 
very good type of heating plant for small residences. 
In the case of the hot air furnace the heat is carried 
to the room by convection, as all heat is carried from 
the furnace by the air which passes around the fur- 
nace and enters the rooms from the flues. This air 
circulates in the room and heats the objects and air 
in the room. The efficiency of the hot air system 
will vary, depending on the relative proportion of the 
air taken from outside and upon the temperature of 
the air entering the room. If the cold air entering 
the furnace is taken from the house itself and not from 
outside, the efficiency of the hot air furnace will be 
almost the same as that of a steam furnace; that is, 

31 



Notes on Heating and Ventilation 

from TO to To per cent of the heat of the coal will 
go into the rooms. If, however, the cold air is taken 
from outside, then the heat used in heating the air 
from the temperature of the outside air to the tem- 
perature of the room will be lost, and under ordinary 
conditions of operation the efficiency would be from 
50 to 60 per cent. 

Steam Heating Direct. — From the standpoint of 
ventilation direct steam heat has little advantage over 
a stove, as it gives no means of supplying fresh air. 
Its use in general should be confined to rooms which 
require little or no ventilation. Mechanically, how- 
ever, it has many advantages over the stove or the 
hot air furnace. The boiler for a building having 
this form of heating can be located anywhere in the 
basement, and the rooms are free from dirt or gas. 
The modern radiator is easily adapted to almost any 
location in the room, it is not affected by wind or 
local conditions, and a distant room may be heated 
as easily as one close to the furnace. The efficiency 
of the direct steam heating system is less than that 
of a stove, with a well-installed plant from 60 to 70 
per cent of the heat of the fuel will be delivered by 
the radiator to the room. 

Hot Water, Direct. — The application of direct hot 
water radiators as a method of heating is similar to 
that of steam, with the exception that the surfaces 
are at a much lower temperature and hence more 
radiating surface will be required. It has an advan- 
tage over steam in that the temperature of the heat- 
ing surface can be controlled easily, and can be any- 
where from the temperature of the room to 180 
degrees. It also has the advantage that the surface 

33 



Notes on Heating and Ventilation 

of the radiator being at a lower temperature gives off 
more heat by convection and less by radiation. This 
gives the room more nearly the condition of Summer 
and the heating is not apparent to the occupants of 
the room. In the steam radiator the surface is usu- 
ally not less than 212 degrees. The principal disad- 
vantage of this system is in the fact that the circula- 
tion of the system is by natural circulation ; that is, 
the circulation is produced by a difference in weight 
between the water in the hot leg of the system and 
in the cold leg of the system. This difference in tem- 
perature is usually about 10 degrees, so that the 
difference in weight between these two columns of 
water is small and the resulting force producing circu- 
lation is, of course, small. It is necessary to be very 
careful in designing the piping for the hot w^ater sys- 
tem, as the circulation may be easily affected by the 
height of the radiator above the boiler; the greater 
the height above the boiler, the greater will be the 
difference in weight between the two columns of water 
and the stronger will be the force producing circula- 
tion. This system in general requires more careful 
design and construction than the steam system. The 
efficiency of the hot water system is practically the 
same as that of steam, and we may expect to obtain 
in the room from GO to TO per cent of the heat in 
the coal. 

Indirect Steam Heating. — In heating with indirect 
steam radiation cold air is drawn from the outside, 
passed through and around the hot radiator, which is 
usually situated in the basement, and delivered by 
pipes to the rooms to be heated. The rules governing 
the introduction of air into the rooms and the method 

33 



Notes on Heating and Ventilation 

of running pipes is similar to that employed with hot 
air furnaces. The principal advantages of indirect 
steam over hot air are: Each room has a separate 
source of heat, the system is not affected by the winds 
and no dust or obnoxious gases are carried to the 
rooms. 

The air entering the room will always be as pure 
as the air which furnishes the source of supply. The 
source of heat being independent of the position of the 
boiler, it is possible to place the indirect radiator any- 
where in the building and long hot air pipes are not 
necessary. This makes the indirect radiator much 
more efficient and more certain in operation than the 
hot air furnace. The efficiency of this system, from 
the standpoint of coal consumption, will be much less 
than in direct forms of heating and about the same as 
the hot air furnace; that is, from 50 to 60 per cent of 
the heat of the coal will be used effectively in heating. 

Indirect Hot Water Heating. — The application of 
hot water indirect is similar to that of steam and the 
efficiency is practically the same. The use of hot 
water indirects has been much more limited than the 
use of steam indirects. The installation of hot water 
indirects must be done with great care so that each 
radiator will at all times have the proper amount of 
hot water circulation through it. In the hot water 
indirect radiators, if for any reason the water in the 
radiator becomes cooled, the radiator will be in danger 
of freezing. In mild climates this difficulty would 
not be as serious as in locations where the weather is 
extremely cold. 

Fan System of Heating. — In buildings of a public 
or semi-public character, where a large number of 

34 



Notes on Heating and Ventilation 

people are to be assembled in a relatively small space, 
it is necessary to provide adequate ventilation. In the 
systems that have been previously described it is im- 
possible to introduce into the room sufficient quanti- 
ties of air to ventilate the rooms properly. It may 
be said in general that no system of natural circulation 
has ever produced satisfactory ventilation in a room 
occupied by a large number of people; it is necessary 
to provide some means of mechanically circulating the 
air. This is done in the fan system by means of a 
pressure blower or a disc fan. 

In the fan system the pressure produced by the fan 
makes the circulation so positive that it is not aflfected 
by winds or by the distance of the room from the fan 
itself. The air is taken from the outside, passed 
through the heating coils and forced into the building 
by the fan. 

There are two general methods of heating and ven- 
tilating with the fan system. In one system the air 
is first passed through a tempering coil, then taken 
by the fan and delivered through a heating coil. Each 
room has a connection both to the hot air and to 
the tempered air chamber. The temperature of the 
air in the room is adjusted by taking the air either 
from the hot air chamber or from the tempered air 
chamber. In the second system the rooms them- 
selves are heated by means of direct radiation and 
the fan delivers air to the rooms only for the purpose 
of ventilation. In this case no heating coils would 
be necessary. 

In the first method the economy of the system is 
low, as owing to the large amount of air required 
for ventilation and the quantity of air introduced into 

35 



Notes on Heating and Ventilation 

the room is ordinarily greater than is necessary for 
the purpose of heating the room. The economy of this 
form of fan system depends very largely upon the 
amount of air necessary, but in most cases its effi- 
ciency would not exceed from 40 to 50 per cent; that 
is, only 40 to 50 per cent of the heat units in the 
coal would be effective in heating. In the combined 
fan system, where direct radiation is used for heat- 
ing and the fan system for ventilation, the economy 
of the system is better, probably from 50 to 60 per 
cent. 

The increase in economy of this system is due to 
the fact that it is necessary to run the fans only when 
it is necessary to ventilate the building. 

Combination of Different Systems. — In addition to 
the combination just described, of direct radiation and 
fan ventilation, there have been devised innumerable 
combinations, combinations of direct and indirect 
steam, direct and indirect water, water and hot air, 
steam and hot air. Probably the combinations which 
have been most used have been combinations of direct 
and indirect steam and the combinations of hot water 
and hot air. 

The Economy of Different Systems. — The economy 
of any heating system depends upon the completeness 
with which the coal in the furnace is burned and the 
heat lost by the chimney and the ventilating flues. 
If, with each of the above systems the coal was com- 
pletely burned and all the heat given off were used, 
then each one of the systems would have perfect 
efficiency. 

The losses from any system, given in detail, are as 
follows : Loss through imperfect combustion of coal, 
through the escape of hot gases up the chimney and the 

36 



Notes on Heating and Ventilation 

loss of Jieat in the air passincr up the ventilating fine. 

If the furnace is properly constructed and insures 
good combustion, the loss due to imperfect combustion 
is small. The loss of heat passing up the chimney will 
depend upon the temperature at which the gases leave 
the chimney and the amount of air used to burn a pound 
of coal. The loss bv the ventilating flue will depend 
upon the amount of air it is necessary to supply to 
the rooms for ventilation. 

If the hot gases leave the heating apparatus at the 
same temperature and the same amount of air is used for 
ventilation, then the efficiency of each system will be 
practically the same. If the rooms are not ventilated, 
then, of course, the loss due to the heat passing up the 
ventilating flues will be saved and the system will be 
more economical. In fact, strictly speaking, the loss by 
ventilation should not be considered as entering into the 
efficiency of the svstem. This loss is entirely independent 
of the system used and depends entirely upon the amount 
of air which must be supplied for purpose of ventilation. 
It is quite obvious that any system involving ventilation 
will require a greater amount of coal. The loss due to 
ventilation is due to the fact that all the heat which is 
given to the air between the temperature of the air out- 
side the building and the air in the room is ineflFective in 
heating and is lost up the ventilating flues. It would 
be poor policy, however, for the designers of heating 
systems to cut down the amount of ventilation in a room 
in order to save coal. In several states there are 
general state laws which require that a certain amount 
of air be furnished each person per hour in school 
buildings and other buildings of a public character. 
The necessity and importance of ventilation will be 
discussed under another head. 

37 



CHAPTER III. 

THE DESIGN OF A DIRECT STEAM-HEATING 

SYSTEM. 

Steam heating is usually done by direct or by indirect 
radiation or by combination of both direct and indirect 
radiation. In small residences occupied by only three or 
four persons it is customary to use only direct radiation. 
The practice, however, is a questionable one, and it seems 
desirable, even in small residences, that some indirect 
radiation be used so as to provide a means of ventila- 
tion. Oftentimes only one indirect radiator is used, 
bringing its air either into the room most used or into 
the main hall so that it may be distributed throughout 
the house. In factories and office buildings where a 
large amount of air is introduced by the opening and 
closing of doors it is customary to use only direct radia- 
tion, and in such buildings this is permissible. 

Nature and Properties of Steam. — In order to under- 
stand thoroughly the operation of a steam heating system 
the nature and properties of steam should be studied. 
Steam is a watery vapor, and as used in ordinary radiator 
practice always contains a certain amount of water in 
suspension, as does the atmosphere in foggy weather. 

When water is heated in a steam boiler the tempera- 
ture is slowly increased from the initial temperature of 
the water to the temperature of the boiling point. When 
the water reaches the boiling point small particles of the 
water are changed from water to steam, rise through the 
mass of water and escape to the surface ; the water is 
then said to boil. The temperature at which the water 
boils depends entirely upon the pressure in the boiler and 

38 



Notes on Heating and Ventilation 

obviously, as the boiling point increases more and more, 
heat is required to produce steam. 

Take, for instance, a given case. Suppose we start 
with water in the boiler at 40 degrees and the pressure 
in the boiler at atmospheric pressure, that is, 14.7 pounds. 
Under this condition it will be necessary to increase the 
temperature of the water in the boiler to 212 degrees, at 
which point water will commence to boil. It will be nec- 
essary to add 212 — 40^172 B. t. u. for every pound 
of water in the boiler. In order to convert all the water 
into steam it will be necessary to supply 965.7 heat units 
for each pound, in addition to the 172 heat units con- 
sumed in raising the water to the boiling point. During 
the operation of boiling, however, the temperature of 
the water remains constant and the 966 heat units added 
in order to change the water at the temperature of the 
boiling point into steam are consumed in separating the 
molecules of water and changing the water from a liquid 
into a gas. This last quantity is termed the latent heat 
and it is the latent heat of water which is used primarily 
in furnishing heat to the room in steam heating. As the 
pressure in the boiler increases the latent heat diminishes. 
The relation of these various quantities has been very 
carefully determined by Regnault and compiled in the 
form of steam tables. The following is an abbreviated 
steam table. More complete tables will be found in Pea- 
body's Steam Tables, or in any of the mechanical engi- 
neering handbooks. 

STEAM TABLES. 

Column 1 of the Steam Table gives the pressure of the 
steam above the atmosphere in pounds per square inch 
and below the atmosphere in inches of mercury. Column 
2 gives the corresponding temperature of the steam. 

39 



Notes on Heating 



and 



Ventilation 



Column 3 gives the heat of the liquid or the heat neces- 
sary to raise one pound of water from 32 degrees to the 
temperature of the boiling point, corresponding to the 
pressure. Column 4 gives the latent heat necessary to 
change a pound of water at the temperature of the boil- 
ing point into steam at the same temperature. Column 
5 is the sum of columns 3 and 4, and represents the 
amount of heat necessary to raise a pound of water from 
32° to the boiling point and then change it into steam 
at the temperature of the boiling point. The quantities 
given in this column are called total heat. Column 6 
gives the volume of one pound of steam at the differ- 
ent pressures. 



Pressure 


TABLE XIV— PROPERTIES OF 


STEAM. 




or Vacuum. 










Volume of 


Inches 


Tempera- 


Heat of 


Latent 


Total 


1 lb. of 


Mercury 


ture 


the Liquid 


Heat 


Heat 


Steam 


—24 


137 


105 


1,019 


1,124 


135 


—20 


160 


128 


1,003 


1,131 


78.3 


—16 


175 


143 


992 


1,135 


55.9 


—14 


387 


155 


984 


1,139 


43.6 


— 8 


197 


165 


977 


1,142 


35.8 


— 2 


205 


173 


971 


1,144 


30.6 


Pounds 












per sq. in. 















212 


180.9 


965.7 


1,146.6 


26.36 


1 


215 


184 


964 


1.148 


25 


2 


219 


188 


961 


1,149 


23 


8 


222 


191 


959 


1,150 


22.3 


4 


224 


193 


957 


1.150.5 


21.2 


5 


227 


196 


955 


1,151 


20.16 


10 


239 


208 


946 


1,154 


16.3 


15 


249 


218.8 


939.3 


1,158.1 


13.7 


20 


. 258.7 


228 


932.5 


1,161 


11.85 


25 


266.7 


236.2 


927.1 


1,163.3 


10.36 


30 


273.9 


243.5 


922 


1,165.5 


9.34 


35 


280.5 


250.2 


917.3 


1,167.5 


8.45 


40 


286.5 


256.3 


913 


1,169.3 


7.73 


45 


292.2 


262.1 


909 


1,171.1 


7.11 


50 


297.5 


267.5 


905.2 


1,172.7 


6.61 


55 


302.4 


272.6 


901.6 


1,174.2 


6.16 


60 


307.1 


277.2 


898.4 


1,175.6 


5.77 


65 


311.5 


281.8 


895.1 


1,176.9 


5.43 


70 


315.8 


286.1 


892.1 


1,178.2 


5.13 


75 


319.8 


290.3 


889.1 


1,179.4 


4.86 


80 


323.7 


294.3 


886.3 


1,180.6 


4.63 


85 


327.4 


298.1 


883.6 


1,181.7 


4.41 


90 


330.9 


301.8 


881 


1,182.8 


4.20 


95 


334.4 


305.4 


878.5 


1,183.9 


4.02 


100 


337.6 


308.9 


876 


1,184.9 


3.83 


110 


343.9 


315.4 


871.4 


1,186.8 


3.57 


120 


349.8 


321.5 


867.1 


1,188.6 


3.33 


130 


355 


327.5 


863 


1,190.3 


3.1 


140 


360 


333.5 


8"59.1 


1,191.9 


2.92 


150 


365.7 


338.3 


855.4 


1,193.4 


2.75 



40 



Notes on Heating and Ventilation 

EXAMPLES IN USE OF STEAM TABLE. 

Example 1. — It is required to convert 10 pounds of 
water at 32° into steam at 100 pounds gauge pressure. 

Solution. — We see from column 5 that the total heat 
of 1 pound of steam at 100 pounds pressure is 1,184.9 
heat units. Then to form 10 pounds of steam would 
require 10 times this amount, of 11,849 heat units. 

2. How many heat units will be required to form 5 
pounds of steam from feed water at 100° in tempera- 
ture into steam at 10 pounds gauge pressure? 

Solution. — The total heat of steam at 10 pounds pres- 
sure above 32° is 1,154 heat units. In this case the feed 
water already contains in it above 32°, 100 — 32 = G8 
heat units. The specific heat of water being 1, the heat 
units required to form a pound of steam will be 1,154 
— 68 ^ 1,086, and to form 5 pounds of steam would re- 
quire 5 X 1,086 = 5.430. 

3. A steam pipe is 8 inches in diameter. The pressure 
of steam in the pipe is 10 pounds gauge. The steam 
pipe is to transmit 1,600 pounds of steam per hour. 
What will be the velocity of steam in the pipe? 

Solution. — From column 6 of the table we see that 
the volumn of 1 pound of steam at 10 pounds gauge pres- 
sure is 16.3 cubic feet. Then 1,600X16.3=26,080 cubic 
feet, the volume of steam passing per hour. This divided 
by 3,600 equals 72, the number of cubic feet passing per 
second. An 8-inch pipe has an area of 50 square inches ; 
50^144=.347 square feet; 72-^.347=208 feet per sec- 
ond, which represents the velocity of the steam passing 
through the pipe. This velocity is very high. Ordinarily 
the velocity in steam pipes should not exceed 100 feet 
per second, even in very large pipes. 

41 



Notes on Heating and Ventilation 

LOSS OF HEAT FROM RADIATORS. 

In designing a direct steam system it will be necessary 
first to compute the heat losses from the various rooms 
by the rules previously given. After these losses are 
determined it will be necessary to place sufficient radi- 
ating surface in the room to supply these losses. In 
order to know the amount of surface that should be 
placed in a room it is necessary to know the amount of 
heat given off per square foot by the different forms of 
radiators. Heat losses for the different forms of direct 
radiators are given in the following table: 

TABLE XV— LOSS FROM WROUGHT IRON PIPE AND CAST 

IRON RADIATORS. 

o B, ^ 

"H *" '^t 

^ ^ 5c 

° "S ftp 

Cast Iron Radiators, 38 

1 column 48 sq. ft. 226 

2 column 48 sq. ft. 226 

3 column 45.3 sq. ft. 226 

6 column 36 sq. ft. 225 

Wrought Iron Radiators, 

1 column 12 sq. ft. 221 

2 column 42 sq. ft. 222 

3 column 48 sq. ft, 229 

4 column 48 sq. ft. 226 

1" wall coil, 1 pipe high 212 

1" wall coil, 4 pipes high 228 

Colonial wall coil 212 

Column 5 is the column which shows the relative effec- 
tiveness of the various types of radiators. It is obtained 
in the following manner: Take, for example, the two- 
column cast iron radiators, results of which are given in 
line 2 of the table. A pound of steam at 226°, as we see 
from the steam tables, gives up its latent heat in con- 
densing which amounts to 965 heat units. This radiator 

42 





S cr r 


-M 


hr 


1 rQ 


o^ 






T! 


•^Oj 






d- 






(D 




m 




£o3 


5 P 


P3 


u 


Oi 




.-o o 


<D 




(D 0) 




Cfi (L r; 


P. 


u 


-M -M 


2 !« 


X5 W 




n 




a*- 

g 0) O 


<S Of 


P 


o 




c5 . 




u 


fc^o 


h^£ 


K, C 4J 


P3 


<1J— s o 


Inches. 










105 


.212 






1.82 


76 


.253 






1.65 


88 


.204 






1.42 


71 


.217 






1.35 


38 Inches 










89 


.446 






3.27 


83 


.284 






2. 


70 


.294 






1.77 


73 


.202 






1.27 


70 


.41 






2*. 8 


65 


.425 






2.48 


70 


.330 






2.25 



Notes 



o n 



Heating and 



9^^ 

Ventilation p 



condensed .253 pounds of steam per square foot of sur- 
face i)er hour. Then 905 X --53=247, tlie heat units 
given up by the radiator per square foot per actual sur- 
face per hour. The steam in the radiator was at a tem- 



tm*-*^^ 




Fig. 9. Single-Column Cast Iron Radiator. 

perature of 226° and the air in the room at a tempera- 
ture of 76°, the difference in temperature being 150°. If 
we divide 247 by 150 the result is approximately 1.65. 
71-iis result represents the B. t. u. transmitted per 

43 



Notes on Heating 



and 



Ventilation 



square foot of rated surface per hour per degree differ- 
ence of temperature between the steam inside the radi- 
ator and the air in the room. This is the quantity which 
should be used in comparing the relative merits of the 
various forms of heating surfaces. 

The results of a series of experiments made at the 




O O 

d/ngf/e Co/i/mr?. 



D O O 



O O 



poo 



Fig. 10. 

University of Michigan, extending over a period of 
a number of years, together with the results shown 
in the foregoing table, lead to the following conclusions : 
Different Types of Relative Efficiency. — Radiators 
zvith different steam I'olumes do not give essentially 




44 



Notes on Heating and Ventilation 

different results, except as the volume is so small as 
to restrict the passage of steam. Single column radi- . 

ators, as shoivn in Fig. (), usually show larger results ^^Xj^cu^ 
than those zvith more than one column. • The con-' 
results than those nith more than one column. The con- 
densation per square foot of radiator per degree differ- _ ' 

ence of temperature as shown in column 5 of Table VII 
shows a rapid decrease as the number of columns in-^ 
creases. The reason for this is quite apparent when we 
consider the position of the radiating surfaces in a 
single pipe radiator as compared with the surface in a 
three-pipe radiator. Referring to Fig, 10, tube B, you 
will note that this tube can radiate heat in all directions 
without interference, except those lines which radiate 
to columns A and C. Columns A and C being at the 
same temperature, no radiant heat passes between them, 
so that all the surface of column B which would radiate 
its heat to columns A and C is unaffected. The amount 
of surface which does this, however, is extremely small. 
Suppose we take point 1 on column B. The heat 
from that point radiates in a straight line in all direc- 
tions. But all the rays of heat between ray 2 and ray 3 
strike on column A and are lost because column A is 
the same temperature as column B. The number of rays 
that do this are extremely small in a single column 
radiator. 

If we consider column B in a three-column radiator 
and take point 1 on column B we see that all the rays 
between 2 and 3, 4 and 5, 6 and 7, 8 and 9, 10 and 11 
are lost and become ineffective for heating as columns 
A, C, D, E, F, are at the same temperature and intercept 
rays passing into the room. 

45 



Notes on Heating and Ventilation 

When the cokimns in a radiator have been increased 
from 5 to 6 then the inner cokimns have practically no 
effect in giving off radiant heat, and the only heat they 




Fig. 11. Two-Column Cast Iron Radiator. 

give off is given by convection due to the passage of 
air through the radiator. 

By glancing at Fig. 10 we see that the greater the 
distance between the columns or pipes of a radiator the 
smaller would be the number of rays of radiant heat 

4G 



Notes on Heating and Ventilation 

intercepted by other columns of the radiator and the 
larger would be the radiating effect; the wider the 
space between the columns of the radiator the more 
effective does the radiator become in giving off heat. 

The writer has had opportunity to make a series of 
tests on radiators of the two-column type, having the 
sections of one radiator spaced at 2^/^ inches and the sec- 
tions of the other radiator 3% inches. The increase of 
^ inch in the length of space added approximately 10 
per cent to the effectiveness of the radiator. 

Radiators are made in standard heights. The height 
most used is 38 inches. They can be purchased, however, 
in varying heights from 15 to 45 inches. The radiators 
of various heights are rated at a certain number of 
square feet per section. For instance, a 38-inch two- 
column radiator, as shown in Fig. 11, is rated at 4 square 
feet per section. As a rule, however, radiators are 
slightly overrated. A radiator containing 48 square feet 
has an actual surface, when measured, of about 47 square 
feet in most two-column radiators. In some cases, par- 
ticularly in radiators having a large number of columns, 
the radiators are very much overrated. In one instance 
a radiator rated at 36 square feet had an actual surface 
of only 27 square feet. In purchasing a radiator, there- 
fore, it is important to know that it has approximately 
the surface given in the catalogue of the manufacturer, 
as the radiating power depends primarily upon the square 
feet of surface it contains. 

Comparing lines 2 and G of Table XV you will notice 
that the two-column wrought iron radiator transmits 
about 20 per cent more heat than the two-column cast 
iron radiator. This is undoubtedly due not to the 
difference of material, but to the difference in the spacing 

47 



Notes 



o n 



Heating and Ventilation 



of the columns composing the radiators. Wrought 
iron pipe wall coil, as shown in the next to the last Hne 
of the table, condenses almost 50 per cent more steam 
than the cast iron radiator. The reason for this is not 




Fig. 12. Three-Column Cast Iron Radiator. 

SO much the difference in material as the difference of 
location. In the case of the cast iron radiator the air at 
the base becomes heated, rises along the radiator, becom- 
ing more and more heated as it comes nearer to the top, 

48 



Notes 



o n 



Heating: 



and 



Ventilation 



SO that at the top of the radiator there is a smaller dif- 
ference between the temperature of the air surrounding 
the radiator and the temperature of the radiator itself. 
This reduces the transmission of heat near the top of the 
radiator. In the wall coil, the sections being placed in 
a horizontal position, the air remains in contact with the 
coil for a short time only, so that the air surrounding all 
portions of the coil is practically at the same temperature. 
To state this in another way, in the cast iron radiator, 
with the sections placed vertically, the diiTerence in tem- 





Ua^ 




Fig, 13. Six-Column Cast Iron Radiator. 



End View of Sec- 
tion. 



perature between the air outside the radiator and the 
steam inside the radiator is much less for the whole 
height of the radiator than in the wall coil, where the 
pipes are placed horizontally, making the wall coil much 
more effective per square foot of surface. Approxi- 
mately we can say that a wall coil will do 50 per cent 
more per square foot than a cast iron radiator. Their 
extensive use, however, excepting in shop buildings, is 
always more or less questionable, owing to their unsightly 

49 



Notes on Heating and Ventilation 

appearance and the difficulty of installation in many 
places. 

Flue Radiators — Besides the usual radiator in 
which a large proportion of the heat is given off by radi- 
ation and a smaller portion by convection, there is what 
are known as flue radiators. In a flue radiator each 
section, as shown in Fig. 14, has a projecting flange at 
the outer edge, so that there is confined in the radiator 
itself a series of narrow hot air flues. In these radiators 
only the external surface of the radiator acts as radiating 
surface. The interior surfaces of the radiator act as indi- 
rect radiators to heat the air which is drawn up from 
below the radiator. Table XVI gives the loss by radia- 
tion from the radiator as separated from the loss due to 
the heat transmitted to the air in the flues. 

TABLE XVI. HEAT LOSS FROM FLUE RADIATORS. 

2. Rated surface, square feet 42 

4. Temperature steam 212 

5. Temperature external air 70 

6. Difference between steam and air 140 

7 Condensation per sq. ft. rated surface 227 

8. B. T. U.'s per deg-. diff. per sq. ft. rated surface 1.57 

9. Temperature of air entering flues 70 

10. Temperaure of air leaving flues 152 

11. Cubic feet of air leaving flues per minute 45.77 

12. Average velocity of air leaving, ft. per minute 171.3 

13. Percentage of heat transmitted by flues 45 

14. Percentage of heat radiated 55 

The action of the flue radiator depends upon the design 
of the flues. There should be no point of restricted flue 
area ; that is, the air should be given a free passage from 
the base of the radiator to the top. Flue radiators are 
particularly serviceable in rapidly circulating the air in 
the room and can be used in a large room having small 
window surfaces to assist in heating the air in the room 
more rapidly than is done by the ordinary radiator. The 
flue radiator is also used in connection with ventilation, 
in which case the base of the radiator is closed and is 

50 



Notes on Heating and Ventilation 

connected with the outside air as shown in Fig. 22, 
page 74. This phase will be taken up more in detail 
under the head of ventilation. 

Heat Lost from Radiators Under Varying Tempera- 
tures. — In the foregoing tables it has been assumed 




Fig. 14. Cast Iron Flue Radiator. 

that the heat lost per degree of difference of temperature 
between the steam in the radiator and the air outside the 
radiator was a constant quantity. In general this may be 

51 



Notes on Heating and Ventilation 

assumed as true for the ordinary conditions under which 
radiators operate. Where radiators are operated on very 
high or very low temperatures there is a difference in 
the amount of heat transmitted per degree of difference 
of temperature. Table XVII gives the heat transmitted 
for each degree difference of temperature between the 
steam inside and the air outside the radiator per hour 
per square foot of surface for the two-column cast iron 
radiator 38 inches high. 





TABLE 


XVII. 


HEAT 


TRANSMISSION. 


Difference 


in 




B. t. u. transmitted 


temperature. 




per deg. diff. per hr. 


80 








1.425 


90 








1.455 


100 








1.485 


110 








1.515 


120 








1.55 


130 








1.59 


140 








1.635 


150 








1.665 


160 








1.71 


170 








1.745 


180 








1.77 


190 








1.815 



For ordinary conditions of operation — that is, when 
the steam is at from 1 to 5 pounds pressure and the 
temperature of the room is 70 degrees — there will be no 
necessity to consider this variation in the transmission 
of heat due to differences of temperature between the 
steam and the air. There are, however, conditions in 
drying rooms and similar places that are to be kept at 
a very high temperature, where this will make an ap- 
preciable difference in the amount of radiation to be 
used. In vacuum systems also, where a very low 
vacuum is carried, it would be necessary to take these 
factors into consideration. 

Painting may have an appreciable effect upon the heat- 
ing transmission through a radiator. The effect of 
painting is entirely a surface effect, as the number of 
coats of painting on a -radiator produce very little dift'er- 

52 



Notes on Heating and Ventilation 

ence. The heat transmission depends upon the last coat 
put on. A series of experiments carried on recently 
showed the following relative transmission : 



TABLE XVIII. RELATIVE VALUE OP RADIATOR PAINTS. 



Kind of Surface. 

Bare iron surface 

Copper bronze 

Aluminum bronze 

Snow White Enamel 

No Luster Green Enamel. 

Terra Cotta Enamel 

Maroon Glass Japan 

White Lead Paint 

White Zinc Paint 



Relative Transmission. 

1. 

76 

752 

1.01 

956 

1.038 

997 

987 

1.01 




Fig. 15. 



Installation of Direct Radiators. — The following 
suggestions apply to the placing of radiators in the room. 
The radiators should he placed in the coldest portion of 
the room. In general it is best to place the radiators in 

53 



Notes on Heating and Ventilation 

front of the window, selecting a radiator of such height 
that the top will be an inch or two below the window 
sill. There are a number of advantages in placing the 
radiator in front of the window. Probably the most 
important is the fact that it reduces the strong cold down 
draft along the window surfaces. 

Figure 15 shows the effect upon the circulation of the 
air by placing the radiator in front of the windows. In 
this case we get two separate currents of air. The cur- 
rent rising from the radiator divides, one current pass- 
ing out into the room, being cooled by the wall surfaces 
and objects in the room, dropping down to the floor and 
passing back along the floor to the radiator; the other 
current, passing directly to the cold wall surface, is 
cooled, drops down along this surface and comes back 
to the radiator, making the circulation along the cold 
walls and windows close to the radiator a local one which 
does not affect the occupants of the room. 

Carpets and rugs should not extend under the radiator. 
If a radiator is allowed to stand upon a carpet or rug 
for any great length of time, the heat from the legs of 
the radiator will eventually deteriorate the fabric of the 
rug. In a carpeted room the radiator may be placed upon 
a hardwood or a marble base. 

When radiators are placed next the wall a space of 1^ 
inches at least should be left for the circulation of air 
behind the radiator/ 

Unless otherwise specified, radiators are usually tapped 
as in Table XIX. 

TABLE XIX.— RADIATOR TAPPINGS. 

For one-pipe work radiators containing — Inches. 

24 sq. ft. and under 1 

From 24 to 40 sq. ft 1% 

54 



Notes on Heating and Ventilation 

Fi-om 40 to 100 sq. ft 1 1/2 

Above 100 sq. ft 2 

For two-pipe work radiators containing — 

48 sq. ft. and under lx% 

From 48 to 96 sq. ft 11/4x1 

Above 96 sq. ft l^/^xlii 

Rules for Direct Heating.— The best method of 
figuring radiating surface is to determine the actual heat 
loss from the room in B. t. u., for the form of 
radiator which you propose to use. Suppose, for 
example, that a two-column cast iron radiator is selected. 
The steam pressure to be carried is 5 pounds. The tem- 
perature in the room is required to be 70 degrees. Re- 
ferring to the table of heat losses from direct radiators 
(Table XV), we see that a two-column cast iron radiator 
loses 1.65 heat units per degree difference of tempera- 
ture per square foot of rated surface per hour. The 
temperature corresponding to 5 pounds pressue of steam 
as given in Steam Table (Table Vl), is 227 degrees, and 
0/ the difference between this and the temperature of the 
^ room will be 157 degrees. Then the heat lost will be 
1.65>^i57=259jieat units per square foot per hour. Di- 
vidmg the heat loss as given by the rule for loss of heat, 
by 259 gives the number of square feet of radiation to be 
used. 

This is the only method that can be used at all in rooms 
where conditions are exceptional. For rooms of ordi- 
nary construction, heated to 70 degrees, and an outside 
temperature of 0°, a large number of thumb rules are 
used. Some of these thumb rules are as follows : 

In the following rules the expression wall surface 
means exposed wall surface, that is, those surfaces which 
have outside air temperature on one side and room 
temperature on the other side. 

Rule 1. Dh'ide the volume of the room by 55. Add 

55 



v^ 



Notes on Heating and Ventilation 

one-fourth of the exposed zvall surface; add the glass 
surface, and multiply the sum of these t^hree quantities 
by .28. The product zvill be the direct radiation in square 
feet. 

Rule 2. — For ordinary rooms. Divide the exterior 
zi^all surface by 4, add the glass surface and multiply the 
sum by .4. 

B. — For entrance halls. Diznde the exterior zvall sur- 
face by 4, add the glass surface and multiply the sum 
by .54. 

C. — For the zi^all surface in basement rooms below the 
ground line. Divide the zvall surface by 4 and multiply 
the result- by .17. 

D. — For floors having unheated space beloK'. Divide 
the -floor space by 4 and multiply the residt by .23. 

Rule 3. Divide the volume of the room in cubic feet 
by the factors given below and the quotient zmll be 
the radiating surface in square feet. 

First Hoor rooms, tzvo sides exposed 50 

First floor rooms, three sides expose 45 

Sleeping rooms, second floor 60 t^o 70 

Halls and bath rooms 50 

First Hoor rooms, one side exposed 55 

Offices 50 to 75 

Factories and stores 75 to 150 

Assembly halls and cJiurches 75 to 150 

Rule 4. (Baldwin's Rule). — Divide tJie differences 
betzt'een the temperature at zvhicJt the room is to be kept 
and i^hat of the coldest outside temperature by the differ- 
ence betzt'een the temperature of the steam in the radiator 
and that at zuhich you zvish to keep the room and the quo- 
tient zvill be the square feet of radiating surface to be 
allowed for each square foot of equivalent glass surface, 

56 



Notes on Heating and Ventilation 

By equivalent glass surface is meant the wall surface 
divided by 4 plus the glass surface. 

In all of these rules the factors to be allowed for ex- 
posure should be applied. These factors are given under 
the head of "Factors for Exposure." Where the rule 
does not involve the contents of the room it will be neces- 
sary in very large rooms or in rooms where the wall 
surface is very small in proportion to the contents of the 
room, to add a certain proportion of radiation, usually 
not more than 20 per cent, to allow for heating the air 
in the room quickly when it has once been allowed to 
cool. 

Example (Direct Radiation). — In order to under- 
stand better the methods of determining the heating 
surface required for a given house, it would be best to 
consider a concrete example. Figs. IG, 17 and 18 repre- 
sent the basement, first and second floors of a residence. 
The house is constructed of wood, sheathed, papered and 
clap-boarded on the outside and plastered on the inside. 
On the first floor the rooms are 9 feet 6 inches high and 
on the second floor 8 feet 6 inches high. The windows 
are .6 feet high and the standard size is 3 feet wide. 
Table XX gives the general dimensions of the room and 
the heat losses from the various rooms, assuming the 
temperature of the outside air to be zero and the tem- 
perature of the inside to be 70 degrees. 

TABLE XX.— DIMENSIONS' AND HEAT LOSSES. 



Room. Dimensions. 

Parlor 13'9"xl2'9"x9'6" 

Sitting room 14'3"xl5'6"x9'6" 

Dining room 12'6"xl3'9"x9'6" 

Kitchen 13'0"xl3'0"x9'6" 

Hall 12'9"xl0'0"x9'6" 

Second Floor. 
W. oliamber Il'6"xl3'6"x8'6" 1,320 172 48 10,050 

57 









B.t.u. 








Lost 




Wall 


Window 


Per 


Volume. 


Surface. 


Surface. 


Hour. 


1.665 


216 


36 


9,450 


2,100 


95 


48 


7,035 


1,640 


145 


36 


7.350 


1,610 


249 


36 


10,300 


1,210 


197 


18 


7,035 



Notes 



o n 



Heating and Ventilation 



Alcove 10'0"x 9'6"x8'6" 810 130 40 7,560 

So. chamber 12'6"xl4'9"x8'6" 1,560 172 24 7,035 

N. chamber 13' xl3' x8'6" 1,440 188 24 7,455 

Bath 6' x 8' x8'6" 410 50 18 3,150 

E. chamber 13' x 8' x8'6" 880 160 18 5,250 

Front hall 14' x 4' x8'6" 885 33 18 2,730 

8' X 6' x8'6" 

TABLE XXI.— RESULTS OP COMPUTATION, DIRECT SYSTEM. 

Radiating 

B.t.u. B.t.u. Surface. Two Radiating 

from Corrected for Column Cast Surface 

Table XXI. for Exposure. Iron Sq. Ft. by Rule 3. 
First Floor. 

Parlor 9,450 10,395 39 33.5 

Sitting room.. 7,035 7,035 27 38 

Dining room... 7,350 8,085 30 30 

Kitchen 10,300 10,300 39 32 

Hall 7,035 7,770 29 24 

Second Floor. 

W. chamber... 10,050 11,055 42 22 

Alcove 7,560 8,316 31 13 

S. chamber 7,035 7,035 27 26 

N. chamber.... 7.455 8,190 31 24 

Bath ,150 3,465 13 7 

E. chamber... 5,250 5,250 20 14.7 

Halls 2,730 • 3,003 12 14.7 

The method used in determining the British thermal 
units lost from the room is as follows : In Table XII a 
wall constructed as described loses .25, Table XI gives 
the loss from the glass surfaces as 1.03. Then multiply- 
ing the wall surface by .25 will give the B. t. u. lost 
per square foot per degree difference and each square 
foot of glass surface loses about one B. t. u. per square 
foot. Take, for example, the parlor. The wall surface 
is 216 square feet. Multiply this by .25; the result, 54 
B. t. u. lost per square foot per degree difference of 
temperature. Add the loss from the glass surface, 36 B. 
t. u., makes a total loss of 90 B. t. u. Multiply- 
ing this by the difference between the outside and the 
inside temperature, gives the heat lost, or 90 X '^0=6,300 
B. t. u. lost from the room per hour. To this must 
be added the loss through the wall by leakage which has 
been assumed to be 50 per cent, making the total loss 
9,450 B. t. u. 

In Table XXI the second column gives the B. t. u. 

58 



Notes 



o n 



Heating and Ventilation 



as determined in Table XX ; the third column the B. t. 
u. corrected for exposure, 10 per cent being- added to 
rooms having north and west exposures, as, in this case, 
the prevailing v^inds are from the west. Column 4 gives 




Fig. 16. Basement Plan. 



the radiating surface required to heat the rooms with a 
two-column cast iron radiator. Column 5 gives the 
radiating surface as determined by Rule 3. 

59 



Notes 



o n 



Heating and Ventilation 



The quantities in column 4 are obtained in the fol- 
lowing manner. The steam pressure to be carried in the 
radiator is 5 pounds. The corresponding temperature 




Fig. 17. First Floor. 



of steam is 227 degrees. The temperature of the room 
is 70 degrees. The difference in temperature between the 
room and the steam will be 157 degrees. In the last 



60 



Notes 



o n 



Heating and Ventilation 



column of Table.^VJJLthe heat lost for a two-column cast 
iron radiator is given as 1.65 B. t. u. per degree differ- 
ence per hour. Then the total heat lost per square foot 
per hour will be [l57Xl-65=2G0 B. t. u.T that is, each 
square foot of radiator surface will give to the room 




Fig. 18. Second Floor. 

260 heat units per hour. Dividing the heat lost from 
the room, as given in column 3, by 260, will give the 
results shown in column 4. 

In column 5 th& radiating surface has been deter- 
mined by Rule 3, which is sometimes called the Volume 



5** ^ 



61 



Notes on Heating and Ventilation 

Rule ; that is, the cubic contents of the rooms are divided 
by a certain factor, depending upon the location of the 
room. A careful comparison of columns 4 and 5, 
together with an inspection of the plans, will show the 
inconsistency of the volume rule. The volume rule can 
be used only where the room has an average amount of 
cubic contents, as compared with its wall surface. To 
get the best results it is better to employ the method 
that has been used in determining the results in column 4. 
The case often arising where a contractor guarantees 
to heat a building to 70° when the outside temperature is 
zero. When the plant is finished the temperature out- 
side is many degrees above zero. What temperature 
should the rooms heat to under this higher outside tem- 
perature in order to have the room heat to 70° in zero 
weather? 

Assume ti=temperature of the outside air from con- 
tract conditions usually 0°. 

t2=temperature of air in the room which was 
guaranteed by contractor. 

t3=temperature of steam in the radiator during 
test. 

t4=actual temperature outside air during test. 

tg^computed temperature of room for test con- 
ditions. 
The heat loss from the room under contract conditions 

is W 

+G n(t-tO (1) 

4 
Heat loss from room under test conditions is 

W 

+G n(t,-t,) (2) 



62 



Notes on Heating and Ventilation 

Heat loss from radiator under contract conditions = 

(U—U)c (3) 

where c is coefficient of transmission. Heat loss 
from radiator under test conditions = 

(t-t.)c (4) 

Then equation (1) must equal (3) and equation (2) 
must equal (4), hence 



(vv \ '.La— i2;c 
^G )n= and (5) 
4 / t -t, 

( +G)n= . (6) 

V 4 / t.— t. 



Equating the right-hand member of equations (5) 
and (6) we have 



t.— 12 t — t. 



(V 



to— tl t,— t. 

Assuming t^ = 0° and t^=70° and solving for t- 

t,=.695t,+70° (8) 

The following Table XXH has been computed from 
equation 8 and shows the room temperature for dif- 
ferent outside temperature with the same radiation in 
the room and the same steam temperature. 

TABLE XXTI. 

Room Temperaturf! Corresponding' to Temperature of Outside Air. 

Temperature of Temperature of room Temperature of room 



outside air. 


2-column 


1 radia 


tor. 


3 column 


radif. tor, 


—30 




52 






53 


—20 




58 






59 


—10 




64 






64 







70 






70 


10 




77.5 






75 


20 




83 






83 


30 




90 






89 


40 




97 






95 


50 




103.5 






105.5 


60 




110 






108 


70 




117 






115 


80 




123.5 






121.5 


90 




130 






128 


100 




137 






134.5 



63 



Notes on Heating and Ventilation 

Table XXII shows the temperature that should be 
obtained in a room for various outside temperatures, 
the original guarantee being to heat the house to 70 
degrees in zero weather. 

Transmission of Heat Under Various Conditions. — 
The German engineers use the following method of cal- 
culating the amount of heat which will pass through a 
square foot of heating surface per hour. Assume H to 
be the total heat transmitted per hour ; t the difference 
between the average temperature of the hot and cold 
fluids ; c a constant depending upon the kind of surface, 
the hot fluid and the cold fluid and let a ecjual the area 
of the surface. Then 

H = c t a. 
Rietschel gives the following values for the heat trans- 
mitted : c 
From air or smoke through a clay plate 

about ^ inch thick to air 1.00 

From air or smoke through a cast or sheet 

iron plate to air 1.4 to 2.0 

From air or smoke through a cast or sheet 

iron plate to water or the opposite. . . . 2.0 to 4.0 
From steam through cast iron or wrought 

iron plate to air 2.2 to 3.6 

From steam through a metal wall to water. IfiO.O to 200.0 



64 



CHAPTER IV. 

Design of Indirect Steam Heating System. — It is 
seldom that indirect radiators only are installed. This 
is due chiefly to the increased cost of installation and 
operation of such a plant, as compared with a plant 
using both direct and indirect radiation. In a resi- 
dence heated by indirect radiation alone, it will be 
necessary to introduce an' excess of air over that re- 
quired by ventilation. This materially increases the 
cost of operation. In designing an indirect heating 
plant the loss of heat from the building is figured in 
the same way as with the direct system. In using indi- 
rect radiation alone it will be necessary to introduce 
enough air so that the heat left in the room will be suf- 
ficient to take care of the losses from the walls and win- 
dows. In order to determine the amount of surface to 
be placed in the room, it is necessary to know the tem- 
perature to which the radiator will heat the air and the 
amount of heat given off by the indirect radiator under 
different conditions of operation. 

Heat Lost from Indirect Steam Radiators. — The 
amount of heat that may be obtained from a given indi- 
rect radiator will depend upon the temperature at 
which the air is taken in, the temperature of the radi- 
ator, and the cubic feet of air passing through the 
radiator. The following table gives the relation be- 
tween the above quantities, assuming the temperature 
of the air entering the radiator to be zero, the tempera- 
ture of the steam in the radiator 227 degrees, the tem- 
perature corresponding to 5 pounds gauge pressue: 

In school buildings and in buildings where the flues 

65 



Notes 



o n 



Heating and Ventilation 



are of ample size the amount of air passing per square 
foot of radiating surface may be assumed to be 200 
cubic feet per hour. In residences and buildings where 
the flues are usually small, the amount of air passing 






Fia. 19. Extended Surface Indirect Radiator. 

per square foot of surface per hour does not exceed 150 
cubic feet. ^ 

From the results of the tests on indirect radiators 
given, the following points may be noted : 




Fig. 20. Long Pin Indirect Radiator. 

If the temperature of the air entering the radiator 
is constant, then the temperature of the air leaving 

66 



Notes on Heating an d Ventilation 

the radiator will decrease as the amount of air passing 
through the radiator is increased. 

In order to determine the amount of heat trans- 
milted by the radiator it is necessary to assume the 
number of cubic feet of air that will pass through the 
radiator per square foot of radiation. You will also 
note the difference between the extended surface 
radiator and the long pin radiator (Fig. 20). As 
shown in Table XXIII, the temperature at which 
the air is heated by the long pin is less than the tem- 
perature to which the air is heated by the short pin 
with the same quantity of air passing. This is un- 
doubtedly due to the fact that the pins are so long 

TABLE XXIII. HEAT LOSSES FROM INDIRECT RADIATORS. 

X B. t. u. trans- 
mitted per sq. ft. 

Cubic feet Increase In of radiation per 

of air j^;> temperature Pounds of degree dlff. In 

passing 'i'"/ of the air steam con- temper, of air 

per sq. ft. , f passing densed per passing through 

of <^{ the X , sq. ft. of radiator and the 

radiation. '^ _ \ radiator. > radiation. steam. 

- — -- Stan- ^^^^^"""^ Stan- . Stand- 

\ dard Long dard Long dard Long 

A Pin. Pin. Pin. Pin. Pin. Pin. 

50 147 140 .125 .15 .80 .95 

75 143 137 .17 .21 1.17 1.27 

100 140 135 .24 .26 1.51 1.60 

125 138 132 .295 .31 1.85 1.90 

150 135 129 .355 .36 2.22 2.20 

175 132 126 .41 .405 2.57 2.47 

200 130 123 .47 .45 2.90 2.72 

225 127 120 .53 .49 3.25 3.00 

250 123 118 .585 .53 3.60 3.20 

275 121 115 .645 .57 3.90 3.40 

300 119 112 .700 .61 4.22 3.60 

that the ends become cooled. On the other hand, the 
long pin type is a very desirable type to use when one 
wishes to pass large quantities of air, as the radiator 
has ample air passage. This is primarily the work for 
which it is designed. The short pin gives better results 
for ordinary houses where small quantities of air 
pass through the radiator. 

67 



Notes 



o n 



Heating and Ventilation 



Installation of Indirect Radiators. — Indirect radi- 
ators are placed in a chamber or box, usually situated 
in the basement of the building, as close as possible 
to the vertical flue leading to the room which they 
are to heat. The air is admitted to the radiator by a 
duct or flue, connected with the outside air. This duct 
should be supplied with a suitable damper and, if pos- 
sible, be so arranged as to close automatically when 
the steam pressure is taken off the radiator. The cold 
air is usually admitted directly beneath the radiator 
and the heated air on leaving the room is taken off 
at one side. 

TABLE XXIV. INDIRECT RADIATORS— TEMPERATURES OF 

LEAVING AIR. 

Temperature of air Temperature of air 

Temperature leaving the radiator leaving the radiato^r 

of air enter- with a velocity of with a velocity o'f 

ing the radl- 200 cu. ft. of air 150 cu. ft. of air 

ator. per sq. ft. surface. per sq. ft. surface. 

Standard Long Standard Long 

Pin Pin Pin Pin 

130 125 135 128 

10 134 128 139 132 

20 139 132 144 136 

30 144 136 149 140 

40 148 141 153 144 

50 153 144 158 146 

The casing surrounding indirect radiators is usually 
built of galvanized iron and it should be bolted to- 
gether with stove bolts, so that the casing may be 
easily removed. A much better method, but one 
which is more expensive, is to enclose the radiator 
in a small brick chamber with cement floor. This 
chamber should be large enough so that the radiator 
is accessible for repairs. Sometimes a duct is pro- 
vided in the radiator casing so that cold air may be 
taken around the radiator and mixed with the heated 
air through a suitable damper, controlled from the 
room which is heated. This is a very common ar- 

68 



Notes on Heating and Ventilation 

rangement in school buildings. Fig. 21 shows a sketch 
of an arrangement of this kind. 

The pipes or ducts leading from an indirect radi- 




Fig. 21. 
69 



Notes on Heating and Ventilation 

ator should be carried to the room as directl}^ as 
possible. It is better to have a long cold air pipe 
than a short hot air pipe. A long horizontal hot air 
pipe should be avoided. Where the air from the 
indirect radiator is to be used primarily for ventila- 
tion it is best to place the hot air register near the 
ceiling. 

The indirect radiators are usually suspended in the 
radiator chamber on iron pipes supported by rods 
hanging from the ceiling. There should be at least 10 
inches clear space between the radiator and the bot- 
tom and top of the casing. The casing of the radi- 
ator should fit the radiator as closely as possible, so 
that very little air is allowed to pass around the radi- 
ator without being heated. Indirect radiators should 
be placed at least 2 feet above the water line of the 
boiler, if they are to be operated on a gravity system 
of circulation, and should be so arranged that the 
condensed water will drain from them without trap- 
ping. The tappings of these radiators are the same as 
for double pipe direct steam radiators. The following 
table gives the general proportions for an indirect ra- 
diator system : 

TABLE XXV.— SIZE OF FLUES FOR INDIRECT RADIATOR. 

Heating Area of Cold Area of Hot Size of 

Surface, Air Supply, Air Supply, Brick Flue for Size of 

Sq. Ft. Sq. In. Sq. In. Hot Air. Register. 

20 30 40 8x 8 8x 8 

30 45 60 8x12 8x12 

40 60 80 8x12 10x12 

50 75 100 12x12 10x15 

60 90 120 12x12 12x15 

80 120 160 12x16 14x18 

100 150 200 12x20 16x20 

120 180 240 14x20 16x24 

140 210 280 16x20 20x24 

Heating Effect of an Indirect Radiator. — It is usual 
to assume that the air enters the radiator at zero 

70 



Notes on Heating and Ventilation 

degree of temperature, in which case it will leave the 
radiator at about 130 degrees, the steam pressure in 
the radiator being 5 pounds and the velocity through 
the radiator being 200 cubic feet per hour per square 
foot of radiator. Under the above conditions an ordi- 
nary pin radiator will give ofif 470 B. t. u. per 
square foot, or, say approximately, 450 B. t. u. 
Under these conditions the air entering the room will 
be at a temperature of 130 degrees, and if the tempera- 
ture of the room is TO degrees this air will be capable 
of losing to the room 60 degrees, or, in other words, 
there 'is. 60 degrees of temperature available in this 
air for heating purposes, or of 450 B. t. u. given out 
by the radiator 210 B. t. u. are available for heating the 
room. 

SOME RULES FOR INDIRECT HEATING. 

Rule 1. — For ordina/ry rooms. Divide the ivall sur- 
face by 4, add the glass surface, and multiply the sum by 
.6. The quotient will be the amount of indirect radiation 
necessary to heat the room. 

B. — For entrance halls. Diznde the exterior wall sur- 
face by 4, add the glass surface and multiply the sum by 
.75, the product ivill be the number of square feet of indi- 
rect radiation. 

Rule 2. — Figure the heating surface the same as for 
direct heating. Add 40 per cent. 

Rule 3. — Divide the volume of the room by 40. The 
quotient is the square feet of indirect surface required to 
heat the rooms on the first floor. For second and third 
-floor rooms divide by 50, and in stores and large rooms 
divide by 60. 

Example of Indirect Heating. — Take the same house 

71 



Notes on Heating and Ventilation 

that was used in the problem for direct heating. In this 
case all rooms are to be heated by indirect radiation. It 
is in actual practice an unusual arrangement, but it is fig- 
ured out in this way as an illustration merely. 

The heat loss in this house will, of course, be the same 
in both direct and indirect heating and is given in Table 
XXI (p. 58). Assume that the air enters the radiator 
at zero degrees and leaves at 130 degrees ; that the steam 
in the radiator is at 5 pounds pressure and that 200 cubic 
feet of air is passed through the radiator per square foot 
of surface. From the results determined in paragraph 
headed ''Heating Effect of the Indirect Radiator" each [ 

square foot of radiation gives approximately 450 B. t. 
u. If the temperature of the room is 70 degrees only \\,-> 
60 degrees of the heat given to the air is effective in heat- ^ 

ing the room. As the total amount of increase in tem- 
perature is 130 degrees, only approximately 60-i-130, or p 
45 per cent, is available for heating. Each square foot ' ^ 
of indirect radiation gives off .450 B. t. u., 45 per cent 
of 450, or 200 B. t. u., will be available for heating y ' 
the room. The heat loss as given m the table for the 
parlor is 10,395 B. t. u. Dividing this by 200 gives 
52, the number of square feet of radiation required for 
the room. 

TABLE XXVI.— RESULTS OF COMPUTATION, INDIRECT 

STSTEM. 

B. t. u. Size of Volume 

Lost Radiator Area Hot Area of 

Per Hour. in. Sq. Ft. Air Blue. Vent Flue. Room. 
First Floor — 

Parlor 10,395 50 100 12x12 900 

Sitting room 7,035 35 70 8x12 700 

Dining room 8,085 40 80 8x12 720 

Kitchen 10,300 50 100 12x12 1,000 

Hall, 2d floor... 15, 800 73 145 12x12 1,500 

Second Floor — 
W. chamber, 

alcove 19,370 93 180 12x20 1,600 

So. chamber.... 7,035 35 70 8x12 700 

N. chamber 8,190 40 80 8x12 750 

Bath 3,465 17 40 6x 8 800 

E. chamber 5,250 24 50 6x8 600 

72 



Notes on Heating and Ventilation 

Size of Hot Air Pipe. — Fifty-two square feet of 
radiation passing 240 cubic feet of air per square foot 
will pass 12,480 cubic feet of air per hour; 12,480 is 3.47 
cubic feet per second. Allowing a velocity of 5 feet 
per second, the area of the hot air pipe is 3.47-i-5=.69 
square feet. This equals 99 square inches, which is the 
proper area of the pipe. The size of the cold air pipe 
leading to the radiator is usually made the same size of 
the hot air pipe. Table XXVI gives the results for the 
whole house computed in the same manner as given 
above. In the table the odd figures and decimals have 
been left ofif. 

In selecting the size of radiator for a room, it is neces- 
sary to select those that vary by 10 square feet or more, 
as indirect radiator sections are not made smaller than 
10 square feet per section. In a house where the radi- 
ators would be less than three sections, it is necessary to 
put two or three rooms on the same radiator, as it is not 
desirable to make very small indirect stacks. There is 
always danger, however, in taking the heat for two sep- 
arate rooms ofif the same radiator, that the heat will not 
distribute equally between the two rooms. When sep- 
arate rooms are heated from the same radiator, care 
should be taken to see that pipes leading to the two 
rooms have about the same length and as nearly as pos- 
sible the same resistance. 

Combination of Direct and Indirect. — A much more 
common arrangement of indirect radiators is to put in 
just enough indirect radiation to give the proper amount 
of air for ventilation and supply the additional heat for 
the room with direct radiation. Each system is installed 
as though the two were separate, except that they take 

73 



Notes on Heating and Ventilation 

their .steam from the same steam mains and return into 
the same return pipes. In this system the direct radi- 
ators can be installed on the one-pipe system, but the in- 
direct should be installed on the two-pipe system, as in- 
direct radiation does not work well on a one-pipe system. 




Fig. 22. Arrangement of Flue Radiator. 



It is not necessary to put indirect radiation into all the 
rooms of a residence. They are put into the princpial 
living rooms, the hall and the large bedrooms. Where 
the house is small it may be necessary to put indirect ra- 
diation only in the sitting room and in the hall. An ex- 

74 



Notes on Heating and Ventilation 

ample of this kind will be taken up under the head of 
ventilation. 

Flue Radiators. — Where only a small quantity of 
air is needed for ventilation flue radiators may be used in 
place of indirect radiators as shown in figure 22. 

The damper in the outside wall regulates the amount of 
air passing into the room and in extremely cold weather 
this may be entirely closed. Table XVI on page 50 shows 
the heat loss from this type of radiation and the amount 
of air that the flues will pass. In figuring this type of 
radiation figure the same as for direct radiation and add 
25%. Each 30 square feet of flue radiation will furnish 
ventilation sufficient for one person. 



75 



CHAPTER V. 

STEAM BOILERS. 

Types. — Boilers are divided into two general classes 
— fire tube or tubular, and water tube or tubulous boilers. 
The commonest form of boiler used for heating purposes 
in this country is what is known as the return flue fire 
tube boiler. These boilers are adapted to plants of over 
30 and under 150 horsepower and where the pressure 
does not exceed 100 pounds. For pressures above 100 
pounds it is customary to use water tube boilers. There 
is one exception, that is the Scotch marine boiler, which 
is a fire tube boiler and which can be made to with- 
stand pressures of 200 pounds and over in large sizes, 
as in this boiler the fire does not come in contact with 
the outside shell. 

For heating purposes there have been introduced a 
number of special forms of boiler, a great many of these 
forms being built of cast iron. Cast iron boilers are not 
usually operated at pressures exceeding 10 pounds. 

Any of these forms of boilers may be used for heat- 
ing, the selection and the proper form will depend upon 
the conditions in each particular case. In selecting a 
boiler the following points should be taken into consid- 
eration : The boiler must be of sufficient strength to 
withstand the maximum pressure to be carried. This 
does not usually exceed 10 pounds. It must have suffi- 
cient heating surface in proportion to the grate surface 
to be economical. The stack temperature in a low pres- 
sure boiler should not exceed 500 degrees. The boiler 
must have sufficient liberating surface so that the steam 
formed in the water may escape from the surface of the 

70 



Notes on Heating and Ventilation 

water, without carrying a large quantity of water with it. 
The boiler must have large circulating areas so that the 
water may be circulated freely to the heating surfaces 
and the steam formed may pass away from the heating 
surfaces without restrictions. The steam that forms o« 
the heating surfaces rises in bubbles and is liberated from 
the surface of the water. If the boiler has insufficient 
liberating surfaces or the circulating areas are contracted 
the steam cannot rise rapidly enough and bubbles of 
steam remain on the heated surfaces. These bubbles pre- 
vent the water from reaching the heating surfaces and as 
steam is a poor conductor of heat this results in an over- 
heating of these surfaces. This trouble may be very 
serious, especially in the water tube type of boiler, and 
results in the burning out of the tubes. In cast iron 
boilers the lack of proper liberating surfaces and suffi- 
cient steam space often causes excessive priming. The 
question of circulating area and liberating surface is of 
more importance in a low pressure boiler plant than in a 
high pressure plant, as steam at 5 pounds pressure has 
about six times the volurne of steam at 100 pounds pres- 
sure ; so that to have relatively the same circulating area 
and liberating surface in a low pressure boiler, we should 
have five times as much as in a high pressure boiler. 

In boilers for heating purposes it is desirable that they 
should have sufficient steam space, and a large storage of 
water, particularly if the plant is to be continuously oper- 
ated. In boilers having large water storage it is possible 
to maintain a steam pressure on the boiler all night un- 
der banked fires. Where boilers are to be operated only 
occasionally, it may be desirable to have a small quanti- 
ty of water, as each time the boiler is started it is nec- 
essary to heat all tlie w^ater in the boiler before steam is 

77 



Notes on Heating and Ventilation 

formed. The ordinary fire tube return flue boiler, on ac- 
count of its large water storage, liberal circulating areas 
and large liberating surface, is a desirable one for heat- 
ing purposes in large buildings. 

Proportion of Boilers. — The heating surfaces in a 
boiler are those surfaces which have water on one side 
and hot gases on the other. A boiler should be so pro- 
portioned as to transmit as much of the heat generated 
by the fuel to the water as possible. Experience has de- 
termined that for best results in boilers of 50 horse- 
power and over a square foot of heating surface should 
evaporate not more than three pounds of water per 
square foot of heating surface. For small houses, where 
heating boilers of but a few horsepower are used, it is 
not usual to allow a square foot of heating surface to 
evaporate more than 2 pounds of water and when a 
square foot of heating surface evaporates more than the 
amounts given above, the transmission of heat through 
the plate becomes so rapid that all the heat is not re- 
moved ; the result is an excessively high stack tempera- 
ture and a corresponding los^ of heat. Surfaces that 
have steam on one side and hot gases on the other are 
called superheating surfaces. It is not advisable to have 
superheating surfaces in a boiler. 

Small heating boilers are distinctly different from 
power boiler or heating for large plant. In large 
plants coal is being fed to the boiler almost continu- 
ously and the flues are carrying a large quantity of 
gases. Small house heating boilers are fed at infre- 
quent intervals and the flues of these boilers do very 
little of the work of transmitting heat. In small boil- 
ers a distinction must be made between the flue sur- 
face and the fire surface. The fire surfaces are those 

78 



Notes on Heating and Ventilation 

heating surfaces upon which the rays of radiant heat 
from the fire impinge directly. During the periods 
r/hen the drafts are closed most of the steaming in 
the boiler is produced by the fire surface, it is there- 
fore important in a "house heating boiler to have a 
large amount of fire surface as compared with the flue 
surface. It is good practice to have 60 per cent fire 
surface and 40 per cent flue surface in cast-iron house 
heating boilers. 

The proportion of grate surface to heating surface 
depends upon the kind of fuel and the intensity of 
the draft. In small boilers used for heating purposes 
it is usual to allow one square foot of grate surface to 
every 15 to 30 square feet of heating surface. For 
boilers 50 horsepower and over it is usual to allow 
from 30 to 40 square feet of heating surface per square 
foot of grate surface and in very large boilers the 
ratio is 50 to 60 square feet of heating surface per 
square foot of grate. 

The rate of combustion for anthracite coal will 
vary from 2 to 6 pounds of coal per square foot of 
grate surface per hour with average draft. With 
bituminous coal under similar circumstances, 3 to 8 
pounds will be burned in the smaller boilers and 8 
to 15 pounds in the larger sizes. 

The air opening to be allowed in the grates depends 
upon the kind of coal, but usually does not exceed 50 
per cent of the area of the grate. Anthracite and the 
better grades of bituminous coal do not require as 
large opening as do the slack coals. 

The term boiler horsepower as applied to boilers 
has no definite value and varies with local customs, 
and the opinion of the manufacturer. 

79 



Notes 



o n 



Heating and Ventilation 



Boiler Horsepower. — The rating of a boiler should 
be the amount of steam it can evaporate with good 
economy and without producing wet steam. In pur- 
chasing a boil*er specify the number of square feet of 
grate surface the boiler should contain. This is a 
better criterion of the work that the boiler will do 
than the horsepower rating. The American Society 
of Mechanical Engineers has adopted the following 
rating for the horsepower of a boiler: 

A boiler horsepower is 34^ pounds of wat^r evap- 
orated from feed zvater at 212 degrees, to steam at 212 
degrees, which is called the from and at evaporation. 
According to this rule, if three pounds of water are 
evaporated per square foot of heating surface, we would 
allow from, 10 t^o 12 square feet of heating surface for 
each boiler horsepoiver. 

The American Society of Heating and Ventilating 
Engineering recommended the following ratings for 
cast-iron house-heating boilers : 





TABLE 


XXVII. 






Rating of Hovise- 


■Heating Boilers. 




Area 


Coal Burned 


Total Coal 




of 


per Hour 


Burned 


Rating of 


Grate. 


per sq. ft. of Grate 


per Hour. 


Boiler. 


Sq. Ft. 


Lbs. 


Lbs. 




1 


2.67 


2.67 


82 


1.5 


2.96 


4.44 


140 


2 


3.59 


7.18 


226 


3 


4.21 


12.63 


390 


4 


4.55 


18.20 


585 


5 


4.88 


24.40 


780 


6 


5.06 


30.36 


975 


7 


5.24 


36.68 


1,165 


8 


5.36 


42.88 


1,405 


9 


5.48 


49.32 


1,650 


10 


5.60 


56.00 


1,890 


11 


5.71 


62.81 


2,125 


12 


5.82 


69.84 


2,360 


13 


5.93 


77.09 


2,595 


14 


6.08 


85.12 


2,915 


15 


6.23 


93.45 


3.235 


16 


6.35 


101.60 


3,485 


17 


6.46 


109.82 


3,730 


18 


6.51 


117.18 


4,010 


19 


6.55 


124.45 


4,285 


20 


6.58 


131.60 


4,545 


21 


6.61 


138.81 


4.800 



80 



Notes on Heating and Ventilation 

In compiling the table it is assumed — 

1. That the area of the grate shall be the area of 
the opening in which the grate is placed, measured 
to the outermost limits of air openings. 

2. That the boiler is to be used under average 
working conditions, carrying steam at 2 pounds pres- 
sure; that the draft shall be sufficient to burn the 
number of pounds of coal per hour given in the table, 
and that the coal used shall be a good quality of 
anthracite coal having a heating power of 13,000 B. t. u. 
per pound of dry coal. 

3. That the rating as given in the table means the 
number of square feet of direct radiation steam sur- 
face that can be carried by the boiler, based upon the 
supposition that each square foot of direct radiation 
steam surface emits 250 B. t. u. per hour with steam 
at two pounds pressure in the radiator and with air 
surrounding the radiator at a temperature of 70 de- 
grees. 



CHAPTER VI. 

STEAM PIPING. 

In designing a system of steam piping the three fol- 
lowing considerations are the most important : First, 
that the piping shall be so arranged that all condensed 
water shall drain from it ; second, that it shall be free 
to expand, that is, so arranged that the joints shall not 
be strained when the piping is heated ; third, that all 
points in the piping at which air would accumulate shall 
be provided with some means of removing the air. 

In this text the different parts of the piping system 
referred to will have the following meaning: 

Mains. — Mains are those pipes which lead from the 
boiler or boiler header to the submains or risers. Usu- 
ally there are no radiators tapped from these mains. 

Risers. — Risers start from the mains in the base- 
ment or attic, and extend up or down through the build- 
ing. From the risers the connections to the individual 
radiators are taken. 

Returns. — All piping carrying condensed water from 
the steam mains to the boiler is included in the return 
system. The terms return riser, return main, etc., have 
the same significance as in the steam system. 

Reliefs or Drips. — A small pipe connecting the 
steam to the return system so as to carry condensed wa- 
ter to the returns is called a relief or drip. Drips are 
used at all points where water would collect in the steam 
system. These drips are sometimes made of large pipe 
and called equalizing pipes, serving to equalize the pres- 
sure between steam and return mains in gravity return 
systems. 

82 ' ^ 



Notes on Heating and Ventilation 

Pitch. — The pitch of a pipe refers to its indination 
from the horizontal pipe lines. It is best that pipes 
should pitch with the current of the steam, so that the 
steam will assist in the removal of the condensation. 
Return pipes are usually pitched toward the boiler so 
that the system may be drained at that point. 

Water Line. — The water line is the height at which 
the water stands in the return pipes. In a well designed 
gravity system it is seldom more than twelve inches 
above the water line of the boiler. 

Siphon. — When a vertical bend is made in the return 
main so that the return dips down and returns to its 
former level, it is called a siphon. All siphons should 
be provided with a drain (or pet cock). 

Dams. — Sometimes the water level in the boiler is 
lower than that desired in the piping system and an in- 
verted siphon is placed in the return pipe. No return 
will then take place until the water has reached the 
highest point of this bend in the return. A dam should 
be provided with an air cock. 

Water Seal. — Where a return pipe enters the return 
main below the water line it is said to be sealed. It is 
customary to seal all main riser drips and returns from 
indirect radiatprs and pipe coils. 

Water Hammer. — The rattling and the hammering 
often heard in pipes is called water hammer. It is caused 
by steam coming in contact with water or surface in the 
pipes which is colder than itself. A sudden condensa- 
tion results and a vacuum is produced into which the 
water rushes. The blow is often so severe as to crack 
the fittings and spring the valves. It is most apt to oc- 
cur when the plant is first started. Accidents from this 
cause may be avoided by admitting the steam very slow- 

83 



Notes 



o n 



Heating and Ventilation 



ly at first and draining low points in the piping system. 
Steam Traps. — Steam traps are vessels usually placed 
between the steam and the return system to allow the 
water of condensation to be carried to the return sys- 
tem without steam entering the returns. Bv the use of 




Fij. 23. 



steam traps the steam and return mains may have a 
wide difference of pressure. Steam traps are objection- 
able as they are liable to get out of order and require 
frequent repairs. 

Systems of Piping. — The systems of piping may 
be grouped under three general heads. First, the one- 

84 



Notes on Heating and Ventilation 

pipe system. In this system the pipe carrying the steam 
to the radiator also returns the condensed water from 
the radiator to the boiler. Second, two-pipe system, in 
which one set of pipes is used to carry the steam to 
the radiator and an entirely separate set of pipes is used 
to carry the return water to the boiler. Third, a com- 
bination of these two systems. The usual arrangement 
in the combination system is to run the mains on a two- 
pipe system, but the connection between the mains and 
the radiators is on the single pipe system. The one- 
pipe system has certain fundamental advantages over 
the two-pi])e system. In the one-pipe system the steam 
and condensed water are always at the same temperature 
and as a result there is very little opportunity for water 
hammer. In the two-pipe system the steam and water 
being separate the water may become considerably cooled 
below the temperature of the steam, and if at any point 
in the system it again comes in contact with the water 
we have condensation of the steam, vacuum forms, caus- 
ing water hammer. In large plants, however, the one- 
pipe system is not desirable, as it necessitates carrying a 
very large quantity of water in the steam mains. 

One-Pipe System. — The simplest of all piping sys- 
tems used in steam heating is what is known as the one- 
pipe gravity system. In this system, the steam gener- 
ated in the boiler flows through the pipes to the radia- 
tors where it is condensed. The condensed steam in the 
radiators flows back through the same piping system to 
the boiler. This arrangement necessitates the condensed 
steam flowing back against the current of the steam. 
This is objectionable, as there is a tendency to trap the 
water. Because of this tendency it is good practice to 
make the pipes larger in size than would be the case 

85 



Notes 



o n 



Heating and Ventilation 



if the steam and water flowed in the same direction. In 
the one-pipe gravity system the pipe should always be 
given a good pitch toward the boiler. Figure 23 shows 
in diagram the piping and radiator connections for a 
one-pipe system. 

Two-Pipe System. — In the two-pipe system one sys- 
tem of pipes supplies the steam and another system car- 




Fig. 24. 

ries off the water of condensation. The principal object 
in the two-pipe system is to avoid the accumulation of 
any great amount of water in the radiators or mains 
and in that way give a more positive circulation. Fig- 
ure 24 shows the general arrangement used in the two- 



Notes 



o n 



Heating and Ventilation 



pipe system. The indirect radiators and pipe coils 
should always be connected on the two-pipe system. 

Combination System. — In ordinary buildings the 
most satisfactory method is to use a combination of the 
one-pipe and the two-pipe systems. In this system, as 




Fig. 25. 



diagram 



in Figure 25, the radiators 

on the one-pipe system, while 

on tne two-pipe sys- 



shown in 
and risers are 

the mains are installed on the 
tem. The system has this advantage over the one- 
pipe system of mains, that the mains are not obliged 
to carry so much water of condensation and can be freecl 



87 



Notes 



o n 



Heating: 



and 



Ventilation 



from water from time to time. The one-pipe radiator 
connections of this system are more desirable than the 
two-pipe radiator connections in that there is but one 
valve to get into trouble instead of two and the steam 
and the water of condensation are always in contact with 




Fig. 26. 

each other — thus avoiding the danger of water hammer. 
The risers may be one-pipe, as it is very seldom that we 
have difficulty with the circulation in using vertical risers. 
In most cases the one-pipe radiator connections and 
two-pipe mains will be found to giv^ the best satisfac^ 
tion. 

88 



Notes 



o n 



Heating and Ventilation 



Overhead Distribution. — In office buildings and 
buildings where the basement space is valuable for rental 
purposes, it is desirable to place the steam mains where 
they will occupy the least desirable space. It is custo- 
mary to run a vertical steam main to the attic. A set of 
distributing mains is run through the attic, from which 




Fig. 27. 

vertical risers extend down through the building with 
drip pipes connecting to the return system at their low- 
er ends. The radiators are connected to the risers by 
means of single-pipe radiator connections. This system 
gives very satisfactory results as in all cases the cur- 
rents of steam and water are in the same direction. In 
buildings exceeding four stories in height it is usually 
necessary to provide some form of flexible connection 

39 



Notes on Heating and Ventilation 

to allow for expansion. A system of this kind is shown 
in Figure 26. 

Gravity System. — Figures 23-26, inclusive, are all 
shown for gravity return system and this system is the 
one commonly used for all small buildings and for resi- 
dences. In this system the steam and return mains are 
connected to the boiler without the introduction of 
pumps or traps, so that the condensed steam flows back 
to the boiler by gravity. Figure 27 gives a diagrammatic 
sketch of such a system. If the pressure at the surface 
of the water in the boiler is the same as the pressure of 
the surface of the water in the return mains, then the 
water level in the return mains and in the boiler will be 
the same. But if, as shown in Figure 27 by the dotted 
lines, the pressure in the boiler is 5 pounds and the pres- 
sure is only 4 pounds when it gets to the ends of the 
system, then the system is no longer balanced. It is nec- 
essary for the water to rise in the return mains until the 
column of water in the return mains is of sufficient 
height so that its weight will equal a pressure of 1 
pound per square inch, or approximately, it must rise 
about 2.31 feet so that the water in the return main will 
be 2.31 feet higher than the water in the boiler, and 
this will be true for each 1 pound difference in pressure 
between the steam at the boiler and the steam at the ex- 
tremities of the system. It is necessary, then, to be very 
careful to have ample sized piping in this system so that 
the pressure at all points of the return main will be about 
equal. In addition, it is necessary that the steam radia- 
tors, both direct and indirect, be at least 2 feet above the 
water line. For the reasons given above it is not desir- 
able to operate large plants on the gravity return sys- 
tem, as this system requires larger expense for steam 

do 



Notes on Heating and Ventilation 

mains and more or less difficulty will always be experi- 
enced in starting up the system. The systems of circu- 
lation involving traps and pump circulation will be 
taken up under the head of Central Heating Systems. 

Size of Steam Return Mains. — There are a great 
many rules given for determining the size of steam and 
return mains, all of which must be more or less modified 
to meet the particular case in hand. In fact, a very 
careful determination of the size of main is not necessary, 
as, no matter how carefully we calculate the size of the 
main, it is necessary to take the nearest pipe size. In 
determining the size of the main two conditions must be 
considered. First, it must be of sufficient capacity to al- 
low of free circulation. This is the principal considera- 
tion in smaller buildings. Second, the mains must not 
produce more than a certain drop of pressure. This 
point is of particular importance in the design of central 
heating systems. In the case of residences, the size is 
determined by rules determined by practice. In the 
second place, the laws governing the amount of pressure 
in steam pipes are fairly well known. They will be 
treated under the head of Central Heating Systems. The 
most rational method of finding the size of mains is by 
determining the velocity of steam passing in the main. 
Knowing the weight of steam passing in the main and 
having the pressure, the volume of steam passed through 
the main is known. This volume divided by the allow- 
able velocity in feet gives the area of the pipe in square 
feet. The velocities allowed in various forms of mains 
are as follows: 

In the steam engine connections from 75 to 100 feet 
per second. 

In exhaust steam mains from 75 to 150 feet per 
second. 

n 



Notes on Heating and Ventilation 

For steam heating work on the one pipe system, pipes 
2 inches and nnder 10 feet per second. 

For two- pipe work, pipes 2 inches and under 15 feet 
per second. 

For two-pipe work, pipes 2 to 4 inches 25 feet per 
second. 

For single-pipe work, low pressure, pipes 2 to 4 
inches 15 feet per second. 

For single-pipe work, low pressure, pipes 4 inches 
and over 30 feet per second. 

Example. — Assume that a main is to supply 2,000 feet 
of radiation. This radiation gives off approximately 
1.70 B. t. u. per square foot of radiating surface per 
degree difference of temperature. Let the tempera 
ture of the steam be 220°, the temperature of the 
room 70°. Then the total B. t. u. transmitted per 
hour will be 220—70X1.70X3,000=510,000. At 220° 
the latent heat of steam taken from the steam tables 
equals 966 B. t u. Then the steam used per hour 
will be 510,000^966=527 pounds of steam. At 220° 
each pound of steam has a volume of 22.95 cubic feet. 
Hence we have 527X22.95=12,000 cubic feet per hour 
or 3.3 cubic feet per second. For a velocity of 25 
feet per second we must have a pipe with an area of 
.132 square feet or 19 square inches. This is approxi- 
mately the area of a 5-inch pipe. 

Miscellaneous Rules for Size of Steam Main. Rule 
1. — The following is a very common rule for gravity 
return systems: To determine the diameter of the 
main leading from the boiler, point off two places in 
the number expressing the radiating surface and take 
the square root of the remainder. To apply the above 
rule for indirect surfaces, multiply the indirect sur- 

, 98 



Notes 



o n 



Heating and Ventilation 



face by seven-fifths and proceed as for direct sur- 
face. As an example, suppose we are to supply 2,000 
sq^uare feet of direct radiation. We point off two 
places, which gives us 20. The square root of 20 is 
4.48, which would make the size of the main 4^ 
inches. 

Table XXVIII gives the common practice in pipe 
sizes : 

TABLE XXVIII. 

No. of Sq. Ft. Steam 

of Radiation Single Steam Main Steam Riser Steam Riser 

on the Pipe Two Pipe Single Pipe Two Pipe 

Main or Riser. System, System. System. System. 

50 11/^ inch liA inch 1 14 Inch liA inch 

100 2 inch 1% inch 1% inch 1% inch 

150 2 inch 1% inch 2 inch 1% Inch 

200 2^ inch 2 inch 2^4 inch 2 inch 

250 21/^ inch 2 inch 2V2 inch 2 inch 

300 3 inch 2^ inch 3 inch 2h<i inch 

400 31/^ inch 3 inch 3 inch 2 ^^ inch 

500 31/^ inch 3 inch 3 inch 3 inch 

600 31/^ inch 3 1^ inch 

800 4 inch 31^ inch 

1,000 41^ inch 4 inch 

1,500 4% inch 4 inch Very liberal. 

2,000 5 inch iVz inch 

3,000 6 inch 5 inch 

4,000 7 inch 6 inch 

6,000 8 inch 7 inch 

The steam supply of the radiator should never be 
less than 1 inch. Steam mains in one-pipe work 
should not be less than 1^ inches and in two-pipe 
work less than 1}^ inches. The return connections to 
radiators should not be less than ^-inch and return 
mains should not be less than 1 inch. The drip pipe 
should not be less than ^-inch. Long horizontal 
pipes should be one-pipe size larger than the verticals 
in the same line. In the overhead system, especially 
where the building is over seven or eight stories, it 
is well to make the risers fairly large at the lower 
end to take care of the condensed steam. These risers, 
even at the lower end, should not be less than V/2 inches 
in size. 

9^ 



Notes on Heating and Ventilation 



Return Mains. — Return mains cannot be figured for 
returning the water of condensation at a low velocity 
alone, but allowance must be made for the very sud- 
den demands which occur when the plant is started 
and for the air carried with the water. The size of the 
return main is determined almost entirely by practical 
considerations. 

Table XXIX gives the relative size of steam and 
return main and diameter of steam main. 

Pipe Drainage. — Return mains may be placed on 
a dead level, but as a rule it is desirable to give them 
some slight pitch, to some point, preferably the boiler. 
At its lowest point there will be provided some sort 
of drain cock so that all condensed steam may be 
drained out of the system. The radiators, as well as 

TABLE XXIX.— RELATIVE SIZE OP MAINS. 

Diameter Diameter 

Steam Pipe. Return Pipe. 

1^ 1 

2 1 
2% . 1% 

3 1% 

4 2 

6 2% 

6 3 

8 4 

10 4% 

12 5 

the pipes, should be set so that the condensed steam 
may drain from them easily. It is always best to 
drain the condensed steam with the steam, in which 
case the steam tends to free the pipes of the water 
of condensation. If mains are long, it is well to drain 
them at intervals to avoid carrying too much water 
of condensation with the steam. In the gravity return 
system where the drip pipes connect to the return sys- 
tem, there should be at least two feet difference in 
level between the steam main and the boiler water 

94 



Notes 



on Heating and Ventilation 



level, in order to avoid the possibility of the w^ater 
from the boiler being forced back into the steam main. 
Check valves will not prevent it, the water of con- 
densation will accumulate in the return main above 
the check. If it is necessary to drip the steam main 
at a point below or close to the water line, then it 




Fig. 28 



should be drained to a separate system of piping and 
the condensed steam accumulating in this piping 
should be forced back to the boiler by some mechanical 
means. Steam connections to steam mains should al- 
ways be taken from the top of the mains so as to avoid 
the draining of the water of condensation into the con- 

95 



Notes on Heating and Ventilation 

nections. In overhead systems of piping the steam 
mains may be drained directly through the risers as the 
amount of condensation is small compared to the num- 
ber of drain pipes. In this case the risers may be taken 
from the bottom of the main. In connecting radiators 
to the pipe system they should be set so as to have a 
slight pitch in the direction in which they are intended 
to drain. Radiators set so that they cannot be entirely 
drained are a very common source of water hammer. 

Expansion of Pipes. — The expansion of pipes in 
mains exceeding 50 feet in length becomes an impor- 
tant consideration. It is customary to assume that in 
low-pressure steam piping there will be an expansion of 
1^ inches per 100 feet of pipe. In steam mains carry- 
ing a pressure of 80 pounds or over it is customary to 
allow for an expansion of about 1^ inches per 100 feet 
of length. There are three general methods of taking 
up expansion. 

First, a simple means is by making offsets and turns 
in the pipe every 100 to 200 feet, the expansion being 
taken up by the spring in the pipe. This is shown in 
Fig. 28. This method is seldom used except in pipes 
under 8 inches. Another method and the method which 
it is most desirable to use, is to take up the expansion 
at all 90° turns. In this method the pipe when it reaches 
the corner turns either up or down and the expansion 
is taken up by the movement around the vertical nipple 
in the elbows or tees at the corner. This method of 
taking up expansion is shown in Fig. 29. The author 
has had the opportunity of observing a system installed, 
in which expansion amounting to as high as 4 or 5 
inches has been taken up in swing joints of this kind 
and the joints (which have been in use for over twelve 
years) have given no trouble whatever. 

96 



Notes 



o n 



Heating and Ventilation 



The third method is by use of expansion joints. The 
use of expansion joints is in general not to be recom- 
mended. Fig. 30 shows a cross-section of an expansion 
joint. Expansion joints are quite expensive and are al- 
ways liable to leak and require attention. By carefully 
laying out the piping most systems can be installed 
without the use of expansion joints. The most serious 
difficulty occurs in the modern high office building. In 




Fig. 29. 

buildings of not over ten stories expansion joints may 
be avoided by anchoring the risers in the middle so 
that they expand in both directions, and allowing for a 
flexible connection between the risers and supply main 
in the attic and return main in the basement. In this 
case the radiators in the upper and lower stories of the 
building must have allowance made in the radiator con- 
nections for expansion of the main. 

Another method that has been used to allow for ex- 
pansion is by offsetting the pipe at about the middle 
story. As, for example, in a building of say 16 stories, 
run the riser up to the eighth story, then oflfset just un- 
der the ceiling of the eighth story for a considerable 

97 



Notes 



o n 



Heating and Ventilation 



distance, usually not less than 20 feet, and continuing 
the riser up at another location. The principal objec- 
tion to this method is its appearance. In some cases it 
is difficult to avoid the use of expansion joints. In 
using expansion joints, the joint should be anchored so 
that the expansion will go in a definite direction. 

Valves. — A great deal of consideration should be 
given to the valving of a steam heating system. Gate 
valves should be used on horizontal steam mains, as they 




YznzzzzzmzzzzzzzL 



V////////////////.'^ 




Fig. 30. 

do not form a water pocket. If globe valves are used 
on steam mains, they should be placed horizontally, that 
is, in a vertical pipe to avoid forming a steam pocket. 
Where it is possible to use it, an angle valve makes a 
very desirable form of valve. In large buildings where 
the plant will be under the control of an engineer, it is 
desirable to place valves on the steam risers and valves 
on the corresponding return risers. In residences it is 
well to avoid valves, particularly on return mains. A 
valve on the return main is particularly dangerous, as 
it may be closed by accident while the system is in oper- 
ation, in which case the radiator will be filled with 
water and no water will be allowed to return to the 

boiler. 

98 



Notes 



o n 



Heating and Ventilation 



Location of Mains and Risers. — Mains and risers 
should be located in as inconspicuous a place as possible, 
at the same time they should be accessible. The con- 
cealing of mains and risers in the building construction 
is always a questionable practice. If it is necessary to 
conceal the pipe it should be concealed under panels 
screwed on so that they can be removed in case of leak- 
age or other necessary repairs. It is not wise to at- 
tempt to save in risers by making long radiator con- 
nections. The system will give much better operation 







- '/ ^/MeV^ i/i r^t^/i't 'h, '/">■/ ;/ 



Fig. 31. The Simplest Form of Connection. Not Desirable if Ex- 
pansion at Riglit Angle is Great. 

by having frequent risers with shorter radiator con- 
nections. Where risers are concealed in a building of 
wooden construction they should be carefufly protected 
from the woodwork, 

CONNECTIONS TO MAINS AND TO RISERS. 

In making the connections from mains to risers in a 
steam system there are three things to be considered — 
the drip, the expansion, and free circulation. The sim- 

99 



Notes on Heating and Ventilation 

plest form of connection in shown in Fig. 31, and for 
general purposes it is perhaps the best form of con- 
nection. The expansion of the main in the direction 
of its length is taken care of by turning in the threads 
of the vertical pipes. The expansion at right angles 
to the main, which is ordinarily very small, is taken care 
of by the spring of the pipes. If the expansion occurring 
at right angles were very large, then some other form 
of connection would be desirable. 



y?/ser 




'"n\ mill" iiWBijiiiiiiLi Bii]»«/uy<) 

WWWWMWWMIlilHHlMilli nnMiiimrmi iWIKrii 



l^«ll\ 



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Fig. 32. Using a 45° Ell Instead of a 90°, as Shown in Fig. 31. 

Fig. 32 shows a similar connection, but using a 45- 
degree elbow in space of a 90-degree elbow at the main, 
as shown in Fig. 31. This connection offers less resist- 
ance to the passage of steam than the connection shown 
in Fig. 31 ; on the other hand, it does not allow of as 
much expansion. The pipe rising from the main be- 
ing at 45 degrees, there is a limited opportunity for any 
turning in the threads of the pipe and expansion is taken 
up by the spring of the pipe. In this figure a drip is 
shown at the bottom of the riser. A drip is often placed 
at this point, particularly in large buildings. In smaller 

100 



Notes on Heating and Ventilation 

plants condensation is carried back through the steam 
connection itself, as in Fig. 31. In larger buildings it is 
undesirable to carry so much condensation through the 
horizontal pipes and a drip is placed at the bottom of 
the riser, as shown in Fig. 32. 

Fig. 33 shows a connection similar to that in Fig. 31. 
It allows free expansion of the main, the same as Fig. 
31. In Fig. 3'^ all the condensation which has occurred 




Fig. 33. Allows for Expansion of the Main; Requires a Drip at 
the Point where Riser Starts. 

in the main up to this connection will drain into the 
connection and it is therefore necessary to place a drip 
at the point where the riser starts. A connection of this 
kind is often used where it is desired to meter different 
riser connections for different consumers, then the con- 
densation for each riser or each set of risers can be col- 
lected and metered with very little possibility of its com- 
ing back into the main. This is, in some respects, an 
undesirable form of connection. If for any reason the 
water level rises in the return system above the hori- 
zontal pipe connection to the riser, then the riser will be 

101 



Notes on Heating and Ventilation 

entirely sealed from the main and it will be impossible 
to get steam into the riser. The writer has experienced 
this difficulty in places where it was necessary to use this 







Af^j. 



Tf^ser 






^ *:.*!■ :.<'jitt<ii;* a; 



Fig. 34. Often Used in Limited Headroom. Usually Undesirable. 




Fig. 35. A Different Way of Carrying Off the Drip; Used Where 
Drip is Taken Off at End of Main. 

form of connection. This happens particularly in grav- 
ity return systems. 

Fig. 34 shows a form of connection often used where 

108 



Notes on Heating and Ventilation 

there is very limited head room. As a general rule this 
form of connection is a very undesirable one. It allows 
almost no expansion, all expansion in such a connection 
must be taken up in the spring of the pipes. In addition 
to this, if the main happens to carry a large amount of 
water of condensation, part of this condensation may 
flow into the horizontal pipe and impede the circulation 
in the horizontal. Under the same conditions if a con- 
nection such as is shown in Fig. 31 or Fig. 32 were used, 
no difficulty would be experienced. 

Fig. 35 shows another method of carrying off the 
drip. This arrangement is used where the drip is to be 
taken away at the end of the main. It is very often 
desirable at such points, particularly if the main is long, 
to remove the air from the pipe. The figure shows an 
air valve placed at the end of the pipe. Locating an 
air valve at the end of a main near the point of 
the drip facilitates the rapidity of the circulation in the 
main. In a great many installations all the air in the 
system is taken care by means of the radiator air valves. 
Such an arrangement, particularly if the house be large, 
always makes the system slow in circulation. In the 
larger systems it is absolutely imperative that the steam 
mains be properly relieved of air. In addition to making 
the steam slow in circulation, it causes unequal expansion 
of the piping. This trouble will be taken up in another 
chapter. 

Fig. 36 shows the connection of the drips from two 
mains to a single drip pipe. Such an arrangement, while 
simple, is undesirable, as the condensation from one main 
often interferes with the condensation coming from the 
other main. This would give very little trouble if the 
connection were made above the water line. The ob- 

103 



Notes on Heating and Ventilation 



jection, however, to making such connection above the 
water line is that if the two currents of condensation 
which meet at this point are not at the same tempera- 
ture, hammering or a chattering noise results. If placed 




Fig. 36. Drips from Two Mains to a Single Drip Pipe. Simple but 

Undesirable. 

below the line there is an opportunity for the two 
streams of water to interfere with the circulation. 

A better arrangement is that shown in Fig. 37, in 
which the two streams of water coming as drip from 
the steam mains would not strike each other in the same 

104 



Notes on Heating and Ventilation 

line ; the one stream would flow into the other. The 
union of the two streams should occur below the water 
line of the system, if possible. 

Fig. 38 shows a connection from main to riser, in 



Afc 



va/// 




AfC^A 




if/ 



^i^^tf' 



A^^^S'il, 



Fig. 37. A Better Arrangement of Dripping Two Mains into One 

Drip Pipe. 

which the head room is very short and it is desired to 
take up a large amount of expansion, the expansion be- 
ing taken up by a swing on the short vertical nipple and 
by a swing on the riser. This connection has been used 

105 



Notes 



o n 



Heating and Ventilation 



for tunnel mains where the head room in the tunnel did 
not permit of the other forms of connection shown. 

Fig. 39 shows the connection between the main and 
the riser in an overhead system of distribution in which 




/ser 



Fij. 38. Connection from Main to Riser Where Headroom is Very 
Short and Expansion Great. 

the rooms in the upper story are used and it is desired 
to conceal the piping connections. 

As shown in Fig. 39, the connection from the main 
to the riser is carried in the space between the roof and 
the ceiling of the room below. The connection from the 
main to the riser is taken from the bottom of the main. 
This is not objectionable in an overhead system, as each 

106 



Notes 



o n 



Heating and Ventilation 



riser has a drip at the bottom and becomes in itself a 
drip main, and in some cases this is the desirable thing 
to do, as it keeps the steam and main entirely relieved of 
condensation at all points. 




Fig. 39. Connection from Main to Riser in Overhead System of 

Steam Distribution. 



In making connections between mains and risers an 
endeavor should be made to locate the main so that 
the horizontal pipe connecting main to the riser will not 
be too long, just enough to allow for expansion. If it 

107 



Notes on Heating and Ventilation 

is necessary to make this a long pipe, then the pipe 
should be made one pipe size larger than would other- 
wise be used, particularly in the single pipe system. In 
the double pipe system long horizontals are not so ob- 



^B —^m^^ * ''■**• ^H 


i 
f 


H 1 



Fig. 40. Simplest Form; Short; Drains Easily, but Does Not Allow 
for Expansion of Riser. 

jectionable, as the riser may be dripped at its lower end, 
as shown in Fig. 32. 

In residence work it is usually found desirable to 
connect directly from the steam main to the radiators 

108 



Notes 



o n 



Heating and Ventilation 



on the first floor instead of connecting these radiators 
to the risers. This direct connection from the radiator 
to the main insures a quicker circulation of the first 
floor radiators, which is usually found desirable in resi- 
dence work. In building work this is not usually the 




Fig. 41. Horizontal Connection Long Enougli to Care for Some 
Expansion of Riser by the Spring of the Pipe. 

case, the first floor radiators are connected to the main 
risers. 

Radiator Connections. — The connection between 
the radiators and the risers should always be carefully 
considered. There are a great many forms of connec- 
tion used between the radiator and the riser to which it 

109 



Notes 



o n 



Heating and Ventilation 



is connected. Each of these different forms of connec- 
tion has its advantage and disadvantage, which must be 
considered in using any particular type of connection. 
Figures 40 to 46 deal with single pipe work. 

Fig. 40 is the simplest form of connection. Its advan- 
tage is that it is short, simple and drains easily. The 




Fig. 42. Desirable. Clean, but Floor Must Come Up When the 
Trouble-iVIan Comes. 

disadvantage of this form of connection is that it does 
not allow of any expansion. 

The expansion of the riser would lift one end of the 
radiator off the floor and in all probability produce a 
leaky joint. 

Fig. 41 is a similar form of connection, but the con- 
nection between the valve and the riser is long enough 
so that a certain amount of expansion can be taken care 

110 



Notes 



o n 



Heating and Ventilation 



of by the spring of the pipe which connects the radiator 
valve and the riser. 

Fig. 42 is a very common form of connection used 
in residence work. The advantage of this connection 
over the connections shown in Figs. 40 and 41 is that 
where the pipe passes over the floor there is always 
opportunity for dirt to collect around and under the pipe 
and it is difficult to sweep this dirt out. The connection 
shown places the horizontal pipe in the joist space. 




Fig. 43. Similar to Fig. 3, with Position of Radiator Changed. 



The long horizontal pipe under the floor allows a cer- 
tain amount of expansion due to the spring of the pipe. 
On the whole this is a desirable form of connection. Its 
principal objection is that it cannot be easily reached in 
case of accident and it cuts the joists. The most com- 
mon trouble with such connection is to have a sand 
hole in the elbow. Of course to repair this it would be 
necessary to take up the floor. 

Ill 



Notes 



o n 



Heating and Ventilation 



Fig. 43 is practically the same as Fig. 42, the position 
of the radiator being changed. 

Fig. 44 shows the arrangement of radiator connection 
in which the horizontal is dropped down under the ceil- 




Fig. 44. Sometimes Used on Upoer Floors, Horizontal Pipe Ex- 
posed Below Ceilings Is An Objection. Will Do for Store 
Undecorated Rooms. 



ing of the room below. This connection is sometimes 
used on upper floors. The objection to it, however, is 
that the horizontal pipe coming just below the ceiling is 
very unsightly, and it should be used only where the 

112 



Notes on Heating and Ventilation 




Fig. 45. Used iir Office Buildings; Good Form for Fireproof 

Buildings. 




Fig. 46. Commonly used in Residence Work, Where First Floor 
Radiators are Fed from Main In Cellar. 

113 



Notes on Heating and Ventilation 

horizontal pipe is exposed in store-rooms or through un- 
decorated rooms where such pipe would not be objec- 
tionable. 

Fig. 45 is the plan of a connection very commonly 
used in office buildings. The connection is made from 
the riser to the radiator, passing the pipe behind the 
radiator and using a corner valve where the radiator 



1 IV f ^ 
t M II 




Tv' 1 u 



Fig. 47. The Simplest Connection for a Two-Pipe System. 

connection attaches to the main. The principal ob- 
jection to this arrangement is that it throws the radiator 
out some distance into the room and it is very difficult 
to sweep around the connection so as to keep it clean. 
In buildings of fireproof construction and where a large 
amount of expansion is to be taken care of, this is prob- 
ably the best form of connection to use. 

114 



Notes on Heating and Ventilation 

Fig. 46 shows a connection similar to Fig. 44 for first 
floor radiators. It is customary in most buildings to con- 
nect the first floor radiator directly to the main and not 
to a riser. This arrangement is commonly used in resi- 




in Buildings Not More Than Three Stories in Height. 
Fig. 48. Expansion Tal<en Up by Spring in Horizontal Pipes. Used 

dences. The connection is such that we have very easy 
turns and a very slight resistance for the passage of 
condensation. 

115 



Notes on Heating and Ventilation 




Fi3. 49. Radiator on First Floor and Horizontals in Basement. 

116 



Notes on Heating and Ventilation 

Fig. 47 shows the simplest form of radiator connec- 
tion for the two-pipe system. The objection to this ar- 
rangement is similar to the objection made to Fig. 40. 
That is, it is very rigid and will permit of almost no 
expansion and should only be used where the radiator 
is located at such a point that it is not necessary to take 
up expansion. The connection is simple and direct, 
and from the standpoint of circulation, a desirable one. 

Fig. 48 shows a connection in which the expansion is 
taken up by means of the spring in the horizontal pipes. 
The verticals to the radiator valves may be made shorter 
and these connections can all be concealed in the joist 
space if desired. This arrangement can be used for 
buildings not more than three stories in height. Where 
buildings are higher the two-pipe connection should be 
made with a series of elbows, allowing for free expan- 
sion — something like that shown in Fig. 45. 

Fig. 49 shows a two-pipe radiator connection where 
the radiator is on the first floor and the horizontals are 
located in the basement. The same connection is shown 
with a horizontal pipe, allowing for expansion. In this 
case the return connection is shown entering directly 
into the return main without any elbow. This is always 
undesirable, as the connection is very rigid, not allow- 
ing for expansion, and should only be used where the 
connection will not be aflfected by expansion. If expan- 
sion must be allowed for in the return main then a con- 
nection similar to that shown for the steam main should 
be used. 

Fig. 50 shows the radiator connection for automatic 
system of heat control on the double-pipe svstem. In 
this case it is quite common to put the automatic valve on 
the steam supply and the check valve on the return. 

117 



Notes on Heating and Ventilation 

Then when the steam is turned off by the thermostat, 
the check valve automatically closes, and there is no 
possibility of the steam or water in the return main 













■^BL 



Fig. 50. Connection for Automatic System of Heat Control on the 

Double-Pipe System. 



getting back into the radiator. If no check were placed 
upon the return a vacuum would be formed in the ra- 
diator, due to the condensation, and the water would be 



118 



Notes on Heating and Ventilation 

drawn back from the return main into the radiator by 
this vacuum ; then when the steam was again turned on 
this water would cause a severe hammer in the radia- 
tor. A still better arrangement is to put an automatic 
valve on both supply and return. 

In planning radiator connections for a building a long 
horizontal should be avoided, the length should be only 
sufficient to take up expansion. 

The location of the radiator should be carefully se- 
lected, so as not to occupy the best space in the room. 
For example, it is not uncommon to find the radiator 
in a bedroom occupying the only place in the room for 
the bed. The position of the radiators should be select- 
ed also with reference to the risers, so as to make the 
connections as short and direct as possible. The form 
of connection should be such as to allow for proper ex- 
pansion. 

Supporting of Pipes. — Horizontal pipes are usually 
supported by the ordinary form of expansion hanger. 
As a rule pipes should be supported every 10 feet and 
should be supported at points bearing the greatest weight. 
Tn placing a pipe support care should be taken to see 
that each support bears its proper proportion of weight. 
Tn buildings over three stories in height means should 
be taken to carry the weight of the risers. An iron 
strap passing around the pipe and bolted to some 
portion of the building structure is usually the best 
means. Large piping is often supported by chains or on 
brackets with rollers. The supports of large pipes will 
be taken up under the subject of Central Heating. 



119 



CHAPTER VII. 

DESIGN OF A HOT WATER HEATING 
SYSTEM. 

Hot water heating plants may be divided into two 
classes, those using natural circulation, and those using 
forced circulation. In residences and small buildings the 
system using natural circulation is . almost universally 
used. It is simpler in construction and cheaper to in- 
stall and operate. In central hot water heating systems 
and in the larger buildings the forced system of circula- 
tion is employed. It is more certain in circulation, the 
size of the pipes may be smaller and in such buildings 
the system mav be cared for by an expert attendant. 
The systems of forced circulation will be discussed in 
connection with central heating. 

Natural System. — The arrangement of the hot w^a- 
ter boiler and of the piping- in a hot water heating 
plant is similar to that of a two-pipe steam system, the 
difference is onlv in minor changes in the piping system. 
The circulation in a natural hot water heating system is 
produced bv the difference in the weight of the water in 
the cold and the hot leg of the system. It depends verv 
largely upon the height of the water column in the cold 
lee. The difference in the weight of the water in the 
two legs of the system is due to the fact that water 
weiehs less per cubic foot as its temperature is in- 
rreased. namely: 

At 130° the weight of water per cubic foot is fil.56 
pounds. At 140° the weight of water per cubic foot is 
fi1.37 pounds. If, then, there were one cubic foot of 

120 



Notes on Heating and Ventilation 

water in both hot and cold legs of the system with a dif- 
ference of 10° between the two sides, the force to pro- 
duce circulation would be .19 pound. It will be seen 
from this that the force going to produce circulation is a 
small one and may be easily overcome by the resistance 
of the piping system. It is important, then, that in in- 
stalling a hot water system considerable attention be 
given to the arrangement of the piping. 

Loss of Heat from Radiators. — In designing a hot 
water system the losses of heat from the building would 
be computed by the same rules as previously given for 
other systems. These losses of heat having been deter- 
mined, it will be necessary to replace the loss by the 
heat given off by the radiator. In order to determine 
the amount of radiation necessary we must know what 
the losses of heat per square foot are for hot water 
radiators. Table 30 gives the results obtained from hot 
water radiators tested under actual operating conditions 
with hot water. 

Table XXX shows that the rate of transmission, as 
given in the last column of the table, is almost the same 
as for steam radiators. It will be safe to assume that 

TABLE XXX. 

bH C ^ C O, Q, 



S *? 2 o . .o^ 

(V! .C O K . <D . 5 



C iQ 



V. -^ ■^ O . Q,*- 



■O S- e* ft *- hn 

* H H h _: ~ ^ 

38" 3-colnmn cast iron.. 187 182 72 180 ~1 67 

38" 2-column cast iron.. 190 185 70 200 170 

•E' J"^/^<^^^^°^ /•: 182.5 178.5 70 181 LBS 

38 2-column cast iron.. 172.5 167.5 70 150 1.50 

the hot water radiator would give off the same amount 

of heat per square foot whether filled with steam or hot 

121 



Notes on Heating and Ventilation 

water, the temperature inside and outside of the radiator 
being the same. This, however, is not the case, as it is 
customary to operate a hot water plant at a temperature 
not exceeding 180° or less. In calculating heating sur- 
faces, the temperature of the water should never be as- 
sumed higher than 170°. The temperature being about 
220° under ordinary conditions in a steam radiator and 
only 170** in the hot water radiator, the total transmis- 
sion in the hot water radiator is only about 65 per cent 
of the transmission by the steam radiator using steam. 

There is another consideration in hot water heating. 
The lower the temperature of the radiating surface the 
more uniform the temperature of the room and the more 
aereeable the heating effect. Where it is desired to heat 
almost uniformly all portions of a room, regardless of 
initial expense, it may be accomplished by installing verv 
large heating surfaces. The reason for this is easily 
explained. Where the radiating surfaces are kept at a 
hig^h temperature, say 200° or over, at least 50 per cent 
of the heat is given off by radiation and the remaining 
heat is given off by contact of air. When the tempera- 
ture of the radiating surface is lowered a large propor- 
tion of heat is given off by contact of air and a smaller 
portion by radiation. This allows the air in the room to 
be at nearly- the same temperature as the objects in the 
room. It is possible, then, in a hot water system to use 
quite different amounts of radiation, depending upon the 
effect desired. This may be illustrated by an example. 

INDIRECT HOT WATER RADIATORS. 

Suppose a room to lose 10,000 B. t. u. per hour 
and that the heating surface has the same rate of 
transmission whether steam or water is used, and that 

122 



Notes on Heating and Ventilation 

this rate of transmission be 1.5 B. t. u. per square foot 
per degree difference of temperature. In the first 
case, let the room be heated by steam. The tempera- 
ture of steam in the radiator be 220° and the tempera- 
ture of the room 70°. Then the heat loss per square 
foot of surface would be (220 — 70) X the rate of trans- 
mission, 1.5 = 250 B. t. u. The number of feet of radia- 
tion required to heat the room will be 10,000-=-250=40 
sq. feet. 

In the second case, suppose the room to be heated by 
hot water radiator at a temperature of 170°. Then the 
B. t. u. given off per square foot of surface would be 
(170— 70) XI. 50=150. The number of square feet of 
radiation required to heat the room would be 10,000^ 
150=66 square feet. 

In the third case, assume a residence in which a very 
uniform heating condition is desired and the tempera- 
ture of the heating surface is not to exceed 150°. The 
loss per square foot of radiation would be (150 — 70 )X 
1.50=120 B. t. u. The radiation required would then be 
10,000-^120=83 square feet. The amount of radiation 
in hot water heating depends, then, upon the effect de- 
sired. 

In a closed tank system it would be entirely possible 
to obtain a temperature as high as 240° or 250°. In the 
open tank system the temperature should never exceed 
180**, as a higher temperature than this would form 
steam in the tank and there would be danger of the wa- 
ter boiling, which causes a cracking, hammering sound 
in the piping system. 



123 



Notes on Heating and Ventilation 



TABLE XXXI.— INDIRECT HOT WATER RADIATORS. 

The following table gives the emission of heat by indirect hot 
water radiators per square foot per hour per degree difference in 
temperature: 



Velocity of Air in Feet 


British Thermal 


Per Minute. 


Units. 


174 


1.70 


246 


2.00 


300 


2.22 


342 


2.38 


378 


2.52 


400 


2.60 


428 


2.67 


450 


2.72 


474 


2.';6 


492 


2.80 



Tlie difference between 170 degrees (average tem- 
perature of the water in the radiator) and 55 degrees 
(average temperature of the air passing through the 
racHator) being 115, the efficiency at 240 feet velocity 
per minute is 2. B. t. u. per degree difference or 230 
B. t. u. 

Ordinarily the amount of indirect radiation required is 
computed by adding a percentage to the amount of di- 
rect radiation, and an addition of 50 per cent has been 
found sufficient in many cases. When accurate results 
are required it is better to figure the heat loss as given 
in Table XXXI. 

Free area between the sections of radiation to allow 
passage of the required volume of air at the assumed 
velocity must be carefully maintained. The cold-air 
supply duct, on account of less frictional resistance, 
may ordinarily have 80 per cent of the area between the 
radiator sections. The hot air flues may safely be pro- 
portioned for the following air velocities per minute : 
First floor, 200 feet; second floor, 300 feet; third floor, 
400 feet. 

Rules for Hot Water Heating. — Rule 1. — Divide 
the volume of the room by 55. Add ^ of the exposed 

124 



Notes 



o n 



Heating and Ventilation 



wall surface. Add the glass surface. Multiply the sum 
of these by .4, the product will be the square feet of 
direct hot water radiation required. 

Rule 2. — For ordinary rooms divide the exterior wall 
surface by 4; add the glass surface and multiply the 
sum by .55. For entrance halls multiply the sum by .7. 

Rule 3. — Divide the volume of the room in cubic feet 
by the factors given below and the quotient will be the 
radiating surface in square feet. 

First floor rooms, 1 side exposed 40 

First floor rooms, 2 sides exposed 37 

First floor rooms, 3 sides exposed 34 

Second floor rooms 45 — 50 

Halls and bath rooms 35 

Offices 37—50 

In all these rules factors of exposure are to be allowed 
as given on pages 21 to 27. 

In order to imderstand better the methods of deter- 
mining the heating surface required for a given house, 
take the same house as figured for steam on page 77. 

^ABLE XXXII.— RESULTS OF COMPUTATIONS— DIRECT HOT 

WATER. 



B. t. u. 

from 

Table XII. 

First Floor — 

Parlor 10,395 

Sitting room 7,035 

Dining room 7,350 

*Kitchen 10,300 

Hall 7,035 

Second Floor — 

W. chamber 10,050 

Alcove 7,560 

S. chamber 7,035 

N. chamber 7,455 

Bath 3,150 

E. chamber 5,250 

Halls 2,730 

*Just enough radiation 
weather. 



Radiating 




Radiating 


Surface, 


Radiating 


Surface 


2-Column 


Surface 


Actually 


Cast Iron. 


Rule 3. 


Installed. 


68 


45 


68 


46 


52.5 


50 


48 


48 


48 


67.5 


47 


40 


46 


32.5 


48 


65 


39 


65 


49 


18 


40 


46 


34.5 


46 


49 


32 


50 


20 


12 


20 


34 


25 


34 


18 


25 


20 



to keep from freezing in extremely cold 
125 



Notes on Heating and Ventilation 

In Table XXXII the second column gives the B. t. 
u., as determined in Table XXI, column 3. Column 
3 gives the radiation in square feet for a two column 
radiator. Column 4 gives the radiation as determined 
by Rule 3, the volume rule, the volumes of the rooms 
being taken from Table XX. Column 5 gives the radia- 
tion that would actually be used. The quantities in col- 
umn 3 are obtained as follows : Assume the average 
temperature of the water in the radiator is 170°. The 
temperature in the room is 70°, the difference is 100°. 
The rate of transmission as given in Table XXX, line 4, 
is 1.50 B. t. u. The total transmission per square 
foot per hour is, then, 1.50X100=150 B. t. u. Di- 
viding the heat lost from the room, column 2, by 150, 
or the loss for each square foot of radiation, will give 
the results in column 3, the number of square feet of 
radiation required. In column 4 the radiating surface 
has been determined by the volume rule, Rule 3, and 
shows the inconsistency of this method of figuring, though 
it is a method very commonly used. This method 
should never be used except as a check. When the 
volume rule shows very much larger results than the. 
other rules it is well to add surface to the radiator to 
allow for heating the air in the room. This has been 
done in column 5. In regard to proportioning of ra- 
diation one can never trust absolutely to his figures and 
should always carefully compare his results with the 
room and its exposure and use his judgment in regard 
to radiation that seems desirable. 



126 



CHAPTER VIII. 

HOT WATER BOILERS AND PIPING. 

Hot Water Boilers. — Hot water boilers are prac- 
tically the same as steam boilers. Any good form of 
steam boiler may be changed to a hot water boiler by fill- 
ing the steam space with water and allowing the water 
to go in at the lowest point of the boiler and go out at 
the highest point of the boiler. In boilers especially de- 
signed for hot water heating no space is left over the 
tubes, the whole boiler shell being filled with tube sur- 
faces. This makes the hot water boiler more compact 
for the same amount of heating capacity than the steam 
boiler. The circulation in the hot water boilers is prob- 
ably slower than in steam boilers and there is much less 
local circulation. The cold water enters from the bot- 
tom, passes over the tubes and leaves at the top of the 
boiler. The heat transmitted per square foot of surface 
is practically the same in steam and hot water boilers. 
The proportions of heating surface to grate surface and 
of grate surface to chimney area may be taken the same 
for hot water as for steam. 

In large hot water systems the ordinary fire tube boil- 
er is used. The principal modification of the boiler 
would be to fill the steam space with tubes and make 
the return opening same size as the steam opening. 
For residence work cast iron, sectional boilers are usu- 
ally used and these are suitable for all similar work, ex- 
cept where high pressure is used. In high pressure hot 
water heating, cast iron boilers are not permissible, as 
these boilers are not usually made to withstand pressures 
exceeding 20 pounds. A pressure of 20 pounds corre- 

127 



Notes on Heating and Ventilation 

spends to a water column 40 feet high and this is about 
the height of an ordinary four-story building. It is not 
desirable to use cast iron boilers in buildings more than 
three stories high, above that height wrought iron boil- 
ers should be used so as to withstand the static pressure 
due to the height of the water. Cast iron boilers would 
not be suitable for hot water systems using a closed tank 
and having the water under pressure. Boilers for these 
systems are usually made to withstand safely a pressure 
of 100 pounds per square inch. The proportions of cast 
iron boilers for hot water heating are given in Table 
XXXIII. In this table the rating of the boiler does not 
include the piping. In selecting the boiler the square 
feet of radiation equivalent to the piping must be added 
to the square feet of radiator surface. In the average 
house these boilers will carry .6 of their rating in actual 
radiation, exclusive of piping, provided the piping is 
covered w4th some good grade of pipe covering. 

Hot Water Piping. — In designing a hot water 
piping system the most important consideration is the 
resistance of the piping. The resistance of the piping 
should be almost the same for each radiator at the same 
level and the friction of the piping system should be 
kept as low as practicable. 

Definition of Terms Used. — The different parts of 
the piping system referred to will have the following 
meaning : , 

Flow Mains and Risers. — The flow mains and flow 
risers are those portions of the piping system which 
carry hot water from the boiler to the radiator. The 
word Hozv always refers to the hot side of the system. 

Return Mains and Return Risers. — The terms re- 

128 



Notes 



o n 



Heating and Ventilation 



turn mains and return risers refer to piping which re- 
turns the cold water from the radiator to the boiler. 

Expansion Tank. — The expansion tank is a vessel 
partly filled with water and partly filled with air, which 
allows for the variation of the volume of water in the 
system with the changes of the temperature of the water. 
In the open tank system this tank is situated at the 
highest point of the system. In the closed tank system 
it may be located anywhere in the building. 

TABLE XXXIII.— PROPORTION OF CAST IRON HOT WATER 

BOILERS. 
Sq Ft. of 

Radiation Sq. Ft. of Sq. Ft. of 

Boiler Heating Grate Size of Pipe Smoke 

will Carry. Surface. Surface. Connections. Flue. 

150 25 1 2 8 

230 30 1.3 2 8 

375 40 1.6 2^ 9 

500 60 2.5 2% 9 

860 80 3.3 3 9 

1.300 120 5.0 3Mi 10 

2,000 160 6.5 4 11 

2,500 200 8.5 5 or 2-3y2 12 

3,000 250 10.0 6 br 2-4 14 

3,500 280 11.5 6 or 2-4 16 

4,000 330 13.5 6 or 2-5 18 

5,000 400 16.5 7 or 2-5 26 

6,000 500 20 8 or 2-6 22 

7,000 575 23 8 or 2-6 24 

8,000 650 26.5 2-7 or 3-5 26 

9,000 750 30 2-7 or 3-5 26 

10,000 800 33.5 2-8 or 2-6 28 

11,000... 900 36.5 2-8 or 2-6 28 

Pitch. — The pitch of the pipe refers to its inclina- 
tion from the horizontal. 

Legs of the System. — The flow main is often termed 
the hot leg of the system and the return main the cold 
leg of the system. 

Systems of Piping. — Four systems of piping are 
used — the multiple circuit system, the single circuit sys- 
tem, the overhead system, and the single pipe system. 

Multiple Circuit System. — This system is the one 
most used and is sometimes called the standard system 
of piping. This system is shown in Fig. 51. The flow 

129 



Notes on Heating and Ventilation 

main rises from the top of the boiler to a convenient 
height just below the basement ceiling so as to allow 




Fig. 51. 



for pitch towards the boiler of not less than ^ an inch 
in 10 feet. This main or mains is carried around the 



130 



Notes on Heating and Ventilation 

basement so as to supply the risers. Too many risers 
should not be taken from one set of mains, as the radiat- 
ors at the end will be too much cooled. The main 
return is parallel to the flow main and of the same size. 
The open expansion tank is placed at least 3 feet above 
the last radiator and should be connected to the nearest 
riser. The connection to the expansion tank should be 
at the bottom of the tank. In this system the branches 
from the flow main usually supply only one radiator 
on the first floor, a separate branch being run to the 
radiators on the second and third floors. At the points 
A and B, Fig. 51, where the riser branches to go to the 
second floor, the risers offset. This is done to prevent 
too rapid circulation in the radiators above the first floor, 
the tendency being for the second floor radiators to take 
all the water and prevent circulation in the first floor ra- 
diators. This is a reason why it is preferable to connect 
first and second floor radiators separately to the flow 
main. The circulation in the hot water system depends 
upon the vertical weight of the system. The higher the 
main the more rapid the circulation. This makes it neces- 
sary to put additional turns in the risers going to the up- 
per floors or add to the resistance in the piping system so 
as to make the resistance to each floor proportional to the 
effective head producing circulation at that floor. 

Single Circuit System. — In the single circuit sys- 
tem, as shown in Fig. 52, the water flows directly to 
the radiator from the boiler through a pipe, to which 
no other radiator is connected and is returned to- the 
boiler by a separate pipe. A large number of these cir- 
cuits may be connected to one boiler, each one being en- 
tirely separate from the other. This is one of the earliest 
forms of piping systems used for hot water work. It 

131 



Notes on Heating and Ventilation 



gives good results but is expensive to install and makes 
an extremely complicated piping system. 




Fig. 52. 

Overhead System. — The overhead system is shown 
in Fig. 53. In this system the flow main is carried 

132 ■ 



Notes on Heating and Ventilation 



directly from the boiler to the highest point in the sys- 
tem, usually the attic. From this flow main risers ex- 




Fig. 53. 

tend to the basement and connect to the main return. 
This system is sometimes modified as shown in Fig. 54. 

133 



Notes 



o n 



Heating and Ventilation 




In this case the riser in 
both flow and return main 
to the radiator takes its 
supply at a point near the 
level of the radiator and 
delivers the water at a 
point below the level of 
the radiator in the same 
main. One objection to 
this arrangement is the 
fact that the radiators on 
the upper floor will be 
considerably warmer than 
the radiators on the lower 
floors and where this sys- 
tem is installed larger ra- 
diators should be used on 
the lower floors. It has the 
advantage of simplicity. 

Open and Closed Cir- 
cuits. — In the systems de- 
scribed, with the excep- 
tion of Fig. 54, the circu- 
lation from flow to return 
main takes place through 
the radiators. This is 
what is termed an open 
circuit. In the open cir- 
cuit system, where two or 
three radiators are closed 
of, the resistance to cir- 
culation is greatly in- 
creased and the system will be slow to circulate when 
the radiators are opened. This may be avoided by con- 

134 




Fig. 54. 



Notes 



o n 



Heating and Ventilation 



necting up the piping system as shown in Fig. 55. The 
closed circuit system is particularly desirable in large 
buildings, especially buildings having very long hori- 
zontal mains. 

Single Pipe System. — In this system the hot water 
main acts as both flow and return main, the radiators 
being connected on the two-pipe systems as shown in 




Fig. 55. 



Fig. 56. It is necessary in the single-pipe hot water 
system to make the mains very large in diameter, as 
the current in them must be relatively slow. In this sys- 
tem the hot water passes along the top of the main and 
the cold water passes along the bottom of the main. 
It is necessary, then, that the flow riser going to the radi- 
ator be connected to the top of the main and the return 
riser coming from the radiator be connected to the bot- 
tom of the main. The main itself is usually installed on 
a closed circuit, as shown in Fig. 56. The single-pipe 

155 



Notes on Heating and Ventilation 

system of distribution has not been extensively used and 
has not great advantage over the standard system of 
piping-. 




Fig. 56. 



Velocity of Flow. — As previously stated, the hot 
water system should be so designed that the resistance 
of flow to each radiator should be proportional to the 
force producing flow. The water will always seek the 



136 



Notes on Heating and Ventilation 

path of least resistance, so that the radiators having the 
smallest pipe resistance will receive the largest quantity 
of water, and radiators having the largest pipe resistance 
will be proportionally colder. A series of experiments 
have been made at the University of Michigan to de- 
termine the velocity of water in a hot water heating sys- 
tem under actual conditions of operation with full sized 

TABLE XXXIV.— VELOCITY OF HOT WATER CIRCULATION 
(FEET PER SECOND). 

Height of — Difference in Temperature. — 

Circuit in Feet. 10. 15. 20. 

5 .135 .39 .55 

10 .19 .56 .78 

15 .235 .69 .95 

20 .27 .79 1.09 

26 .30 .88 1.22 

30 .31 .96 1.34 

40 .38 1.11 1.53 

50 .425 1.25 L74 

pipes and radiators. The actual velocity was found to 
vary from one-quarter to one-half of the theoretical 
velocity, depending upon the difference in temperature 
between the hot and cold leg of the system. In Table 
XXXIV the actual velocities have been computed from 
the results obtained by these experiments for different 
heights and different conditions of temperature. 

Resistance of Pipe and Fittings. — No complete set of 
experiments has been made to determine the resistance 
of pipe and fittings. The University of Michigan at 
the present time is making a series of experiments, but 
these have not yet been completed. The following are 
the ordinary assumptions that have been made : 



TABLE XXXV.— SIZE OF HOT WATER 


MAINS 




Diameter 




—Total 


Length of Circuit In 


Feet. — 




of mains. 


50. 




100. 200. 




300. 


1 


40 




30 




^ ^ 


1% 


60 




45 30 






m 


90 




60 40 




80 


2 


160 




120 70 




60 


2% 


250 




200 120 




110 


3 


350 




300 200 




190 


s% 


500 




400 330 




250 


4 


650 




500 450 




369 


4^ 


900 




700 650 




600 


5 


1.200 




1,000 800 




650 


6 


1.500 




1.200 1.200 




1.000 



137 



Notes on Heating and Ventilation 

Resistance of standard elbow^25 feet of pipe. 
Resistance of standard tee=25 feet of pipe. 
Resistance of standard return bend=35 feet of pipe. 
Resistance of the ordinary radiator connection from the 

flow main through the radiator to the return main is 

equivalent to about 100 feet of pipe. 

Size of Pipe. — The size of pipe may be figured by 
assuming the actual velocity due to the head and calcu- 
lating the size required to carry a given amount of 
water. This is usually done in large buildings. In 
smaller buildings it is customary to follow the rules 
used in good practice. 

TABLE XXXVI. 
The capacity of mains 100 ft. long, expressed in the number of 
square feet of hot-water radiating surface they will supply, the 
radiators being placed in rooms at 70° Fahr., and 20" drop being 
assumed. 

Diameter of Two pipe One pipe Overhead Overhead Two-Pipe 
pipes. up Feed up Feed Open tank. Closed Open tank. 

Open tank. Open tank. Tank. Indirect, 

12 in. above 
Direct Direct Direct Direct 

Inches. Radiation. Radiation. Radiation. Radiation, boiler. 

114 75 45 127 250 48 

IVz 107 65 181 335 69 

2 200 121 339 667 129 

2H 314 190 533 1,060 202 

3 540 328 916 1,800 848 

SVz 780 474 1,334 2,600 502 

4 1,060 645 1,800 3,350 684 

5 1,860 1,130 3,150 6,200 1,200 

6 2,960 1,800 5,000 9,800 1,910 

7 4,280 2,700 7.200 13,900 2,760 

8 5,850 3,500 9,900 19,500 3,778 

Table XXXV gives the pipe sizes of the mains to 
supply different quantities of direct radiation at different 
distances from the boiler. In establishing the size of 
the risers it is customary to start with a riser the same 
size as the radiator connection and carry the riser down 
to the floor below where the next radiator connects. If 
the radiator does not exceed 60 feet in size, add one pipe 
size to the pipe. 

138 



Notes 



o n 



Heating and Ventilation 



Table XXXVI gives the radiation that may be carried 
by different sized pipes in the different systems. 

Table XXXVII gives the size of risers for various 
quantities of radiation on different stories. 

TABLE XXXVII. 
The capacity of risers expresred in the number of square feet of 
direct hot water radl.ating surface, they will supply the radiators 
being placed in room at 70° Fahr. and 20° drop being assumed: 

Closed Tank 



Diameter of 










Overhead 


Riser 




Open Tank System. 




System. 












Drop risers. 




First 


Second 


Third 


Fourth 


not exceed- 


Inches. 


Floor. 


Floor. 


Floor. 


Floor. 


ing 4 floors. 


1 


. 33 


46 


57 


64 


48 


1^ 


. 71 
. 100 


104 

140 


124 
175 


142 
200 


. 112 


1»^ 


160 


2 


. 187 


262 


325 


375 


300 


2% 


. 292 


410 


492 


580 


471 


3 


. 500 


755 


875 


1,000 


810 



The following are radiator tappings for hot water 
radiators : 

Radiators containing 40 sq. ft. and under 1 inch 

Radiators containing above 40 sq. ft. and not exceeding 

72 sq. ft V4 inch 

Radiators containing above 72 sq ft 1^ inch 

Air Valves, Pitch and Support of Pipes. — Hot water 
piping should be pitched towards the boiler so that the 
water may be drained out of the system at the boiler and 
arrangements should be made so that the water can be 
drained to the sewer. This is necessary on account of 
freezing if the plant is not kept in operation. The ^pip- 
ing should be supported the same as for steam pipes, 
with supports about every 10 feet. Care should be taken 
that the pipes are straight, as any sudden elevation in 
the pipe will form a pocket in which air will collect, and 
this collecting of air in the pocket will prevent the flow of 
water. An accumulation of air in the pipe will stop the 
circulation almost as effectively as a valve. The expan- 

139 



Notes on Heating and Ventilation 

sion of pipes by heat must aiso be taken care of as in 
the steam system. All branches going from the piping 
system and supplying radiators below the level of the 
mains should come off the bottom of the main, so as 
to prevent air accumulating and sealing the pipe. 

All radiators and high points in the mains where air 
will collect should be provided with air valves. 

There are special air valves made for hot water work. 
These will be described later. 



Ml) 



CHAPTER IX. 

VENTILATION. 

Necessity of Ventilation. — The necessity of ventila- 
tion, that is, of renewing the air in a closed room, is due, 
first to the vitiation of the air by the products of respir- 
ation from the persons in the room ; second, to the prod- 
ucts of combustion from artificial illumination ; third, to 
the heat generated by persons and lights in the room ; 
and, fourth, to the presence of gases from chemical 
processes. 

In a small house or a small school building ventilation 
is very easily produced by methods which employ natural 
draft, such at hot air furnaces, steam and indirect radi- 
ators. In all systems using natural draft, the force of 
the draft depends upon the difference of the temperature 
between the air inside and that outside the flue. Where 
this difference amounts to only 30° or 40° the difference 
in the weights of the columns of air is so small that the 
force producing draft is very light and may be easily 
overcome by external conditions. In larger buildings 
it is not possible to use natural draft as the flues be- 
come excessive in size and are not certain enough in their 
operation. This has led to the use in school buildings 
and other public buildings of a forced system of ventil- 
ation in which the circulation is produced by a fan or 
system of fans. 

The perfectness of the ventilation in a room is ordi- 
narily determined by the amount of carbonic acid gas. 
Carbonic acid gas is not poisonous in itself. Its in- 
jurious effects are produced entirely by the reduction of 
the oxygen in the room. There are, however, other in- 

141 



Notes on Heating and Ventilation 

jtirious gases given off from the body, together with 
the carbonic acid gas. 

Products of Respiration. — The lungs take in oxy- 
gen from the air, which combines with the tissues of 
the body, forming the products of combustion which are 
given off by the excretory organs — lungs, skin, etc. The 
principal excretions removed by the lungs are carbonic 
acid gas, water vapor mixed with other gases and some 
animal matter. These excretions, together with excre- 
tions from the skin, produce a disagreeable odor and 
may be poisonous. The average man when sitting still 
consumes in breathing from 19 to 25 cubic feet of air 
per hour, and when exercising from 26 to 35 cubic feet 
per hour. The amount of carbon dioxide and water 
vapor given off per hour by human beings is given in 
Table XXXVIII. 

TABLE XXXVIII.— AIR POLLUTION TESTS. 

Subject to Test. At Work. At Rest. 

Temp. Humid. C02 H20 Temp. Humid. C02 H20 
Deg.F. P.C. Cu.Ft. Grains. Deg.P. P.C. Cu.Ft. Grains. 

Laborer 45 81 1.515 2.03 69 20 .551 1.12 

Laborer ..77 47 1.423 8.05 78 26 .586 2.55 

Clerk 64 44 1.331 1.768 69 29 1.141 1.19 

Draughtsman ..69 41 1.61 1.61 

Average man . . .... .... 66 63 .412 1,365 

Woman 600 

Boy .. .48 

Girl 39 

Products of Combustion. — The products of com- 
bustion from the sources of heating, such as grates, 
stoves, etc., are drawn off by the chimney, but the prod- 
ucts of combustion from the lights in a room pass di- 
rectly into the room. Lights give off carbonic acid gas, 
watery vapor, and traces of sulphuric acid. Table 
XXXIX gives the consumption of combustibles and the 
generation of carbon acid gas by ordinary forms of 
lighting. The table is given for each normal candle 

power. 

142 



Notes on Heating and Ventilation 

TABLE XXXIX.— POLLUTION BY LIGHTING. 

Consumption of Com- Carbonic Acid 

bustible per C. P. per C. P. in 

Source. in Cu. Ft Per Hour. Cu. Ft. Per Hour. 

Gas— Fishtail burner 802— .§27 ~ .494— .304 

Gas — Argand burner — .445 .254 

Gas— Welsbach burner 053— .024 .030— .057 

Petroleum, round burner. ... Gals. .00050 .112 

Petroleum, small flat burner. Gals. .00198 .335 

Wax candles Oz. .271 .417 

Paraffine candle Oz. .324 .459 

Chemical Processes. — The products of chemical 
operations should never accumulate in a room so that 
the odor is perceptible. In some industrial processes it 
is almost impossible to avoid a certain amount of con- 
centration of the gases. In such a case the chemical 
products should be sufhciently dihited with fresh air 
so as not to produce injurious effects upon the occupants 
of the room. 

Table XL gives the relative dilution required for dif- 
ferent gases in cubic feet per 100 cubic feet of air. 

TABLE XL.— AIR DILUTION. 

Detrimental Effect Occurs 

in Several Hrs. in %-l Hr. 

Iodine vapors 00005 .0003 

Chlorine or bromide vapors 0001 .0004 

Muriatic acid 001 .005 

Sulphuric acid .005 

Sulphureted hydrogen .02 

Ammonia 01 .03 

Carbonic Oxide 02 .05 

Carbonic acid 1.00 8.00 

Carbureted hydrogen 6.56 gr. 

Generation of Heat by Human Beings. — The 

amount of heat generated by a human being varies with 
age, activity and temperature of the surrounding air. 
The average amount of heat given off by an adult is 
about 400 B. t. u. per hour, and by a child about 
half that amount, or 200 B. t. u. per hour. Of 400 
B. t. u. given off by human beings about 30 per cent 
is lost by contact of air and about 43 per cent by radi- 
ation, the balance is lost by exhalation and other losses. 

143 



Notes on Heating and Ventilation 

Comparing this with the average steam radiator, we see 
that a child is equal to about eight-tenths of a square foot 
of radiation and an adult man is equal to about one and 
eight-tenths of a square foot of radiation. This becomes 
a very important point in the heating of large halls, par- 
ticularly if they are very crowded and have very little 
external wall space, as the heat given off by the persons 
in the room may be more than sufficient to warm the 
room, which will necessitate providing for the removal 
of this heat from the room. 

Generation of Heat by Illumination. — Ordinarily 
the heat given oft" by electric lights is so small as to be 
negligible, but where oil lamps, candles, or gas lights 
are used, the heat given off is appreciable, except in the 
case of the Welsbach burner, which gives off* relatively 
a small amount of heat. The ordinary fish-tail burner 
is equal to about one and four-tenths square feet of radi- 
ation. 

Table XLI gives the heat generated by different 
sources of illumination per candle power per hour. 

TABLE XLI.— HEAT GIVEN OFF BY ILLUMINANTS. 

Total B. T. U.'s 
Source. Given Off. 

Gas — Fishtail burner 313 

Gas — Argand burner 198 

Gas — V\"elsbach burner 32 

Petroleum 158 

Incandescent lamp 14 

Arc lamp 2.5 

Changes of Air Necessary. — In order that the air 
in a room occupied by human beings may be reasonably 
pure it should be diluted with fresh air. The amount of 
the dilution, except where chemical processes are to be 
considered, is usually determined by the per cent of car- 
bon dioxide present, which is assumed to be proportional 
to the products of respiration. The carbon dioxide itself 

144 



Notes on Heatijig and Ventilation 

is not injurious, but it serves as an indication of the 
presence of other injurious substances. It is usually 
assumed that carbon dioxide is uniformly distributed 
throughout the room. This, however, is not strictly true, 
as carbon dioxide is a very heavy gas and naturally ac- 
cumulates at the floor. Air that contains more than ten 
parts of carbon dioxide to each 10,000 parts of air pro- 
duced by exhalation is of an unhealthful quality. Seven 
parts in 10,000 is ordinarily considered the minimum 
limit of ventilation. The effects of poor ventilation are 
usually shown when the carbon dioxide exceeds six parts 
in 10,000 parts. The following rule may be used to 
determine the necessary amount of air that should be 
supplied to a room : Multiply the number of sources of 
carbon dioxide by the amount of carbon dioxide given 
off from each source. Multiply the result by 10,000 and 
divide by 4. This will give the minimum amount of 
ventilation to be allowed per person. For satisfactory 
ventilation divide by 3. Pure air is found to contain 
about 3 parts of carbon dioxide in 10,000. 

This may be expressed as follows : 
Let S=cu. ft. carbonic acid from each source per hour. 
n=:number of sources. 

a — allowable limit of COo in 10,000 cu. ft. of air. 
A:=the cu. ft. of air to be supplied. 

nS 

Then A=10,000 

a— 4 
a should not exceed 7 and a equals 10 is the sanitary 
limit. 

For example, take a hall containing 400 adults, giving 
off (from Table XXXVIII) .58 cu. ft. of CO, per hour. 



145 



Notes on Heating and Ventilation 

Then to determine the amount of air necessary substitute 
in the above formula 

400X58 

A=10,000 solving 

6—3 
A=770,000 cu. ft. per hour. 

Ordinary Assumption for Change of Air. — The 

amount of air necessary is usually determined by allow- 
ing each person in the room so many cubic feet of air 

TABLE XLII.— CHANGE OF AIR NECESSSARY. 

Hospitals 3,600 cu. ft. per person 

Barracks and workshops 3,000 cu. ft. per person 

Schools 2,400 cu. ft. per person 

Churches, theaters and audience halls 2,000 cu. ft. per seat 

Office rooms 1,800 cu. ft. 

Toilet and bath rooms 2,400 cu. ft. per fixture 

Dining rooms 1,800 cu. ft. per person 

per hour. The changes of air ordinarily allowed are 
given in Table XLII. 

These figures in the above table give sufficient air so 
that the air in the room will remain continuously pure, 
even though occupied all the time. When less than these 
amounts are used there is danger, if the buildings are 
very tight, that the rooms may become foul. The figures 
given above are seldom realized in practice, except 
where the fan system of ventilation is used. In school 
buildings using an indirect system the amount of air 
allowed per child seldom exceeds 1,000 cubic feet of 
air per hour. 

Another method that is sometimes used in figuring 
ventilation, particularly for smaller buildings, is to allow 
so many changes of air per hour. In rooms seldom oc- 
cupied allow the air to be changed about once per hour. 
In living rooms about one and a half to two times 
per hour. In toilet rooms four to five times per hour. 
In restaurants, where smoking is allowed, from five to 

146 



Notes on Heating and Ventilation 

six times per hour. In extreme cases the change of air 
is sometimes as high as ten times per hour. It is diffi- 
cult, however, to change the air in a room very rapidly 
without producing drafts. 

Effects of Poor Ventilation. — The effects of poor 
ventilation have been frequently tested in schools where 
for a short time the ventilation has been cut off. The 
pupils at first complain of being cold, and it is found 
necessary to raise the temperature of the room from 70° 
to 80° before the occupants of the room are warm. 
This is no doubt due to the reduction in vitality owing 
to the impurity of the air, and a lack of oxygen in the 
lungs. After the ventilation has been cut off for a 
period of from 20 to 30 minutes, the pupils begin to 
complain of headache. If the ventilation is cut off much 
longer it is necessary to dismiss some pupils on account 
of headache. 

Systems of Ventilation. — For small residences and 
small buildings where it is not possible to go to 
any great expense for an elaborate system of ven- 
tilation, the best form of heating giving adequate 
ventilation is the hot air furnace. In large houses 
where it is not possible to apply the hot air sys- 
tem, the best system is indrect radiators, either steam 
or hot water. In still larger buildings where the flues 
have a large resistance and it is necessary to supply 
air in large quantities, the only feasible system of dis- 
tributing air is by mechanical means. The usual system 
employed is to draw the air through a series of steam 
coils into a tempered air chamber. In this chamber are 
located the fans. The fan or fans deliver the air through 
heating coils into the building. Systems similar to this 

147 



Notes 



on 



Heating and Ventilation 



have been used where the coils have been replaced by 
hot air furnaces. 

Systems of ventilation using mechanical draft give 
very satisfactory results if properly installed and allow 
of great latitude in the arrangement of the plant. Before 
taking up the details of the systems of ventilation it is 
well to consider certain fundamental facts in the science 
of ventilation. 

Air Inlets and Outlets. — The arrangement of inlet 
and outlet registers in a room should be given very 




Fig. 57. 



careful consideration. They should be so placed as to 
avoid drafts and to insure uniform circulation through- 
out the room. Their position should be such that the 
air cannot pass directly from inlet to outlet flue. The 
creation of drafts may be avoided by bringing the air 
in at very low velocities, particularly where the air 

148 



Notes 



o n 



Heating and Ventilation 



enters so as to strike the occupants of the room. The 
velocity passing through the registers should not exceed 
300 feet per minute; if it is admitted just over the heads 
and where the current of air strikes a person, it should 
not exceed 150 feet per minute. Where the air is 
brought in so that it cannot strike the occupants of the 
room the velocity of air through the registers may be as 
high as 400 feet per minute. 




Fig. 58. 

The most satisfactory arrangement for most rooms 
is shown in Fig. 57. In this figure the inlet register is 
shown near the ceiling. The hot air leaving this regis- 
ter rises to the ceiling, passes along the ceiling to the 
cold window surfaces, where it is cooled and drops to 
the floor; passes along the floor and out the vent flue. 
The inlet register is usually located about 8 feet above 

149 



Notes 



o n 



Heating and Ventilation 



the floor and the outlet register from 4 to 6 inches 
above the floor, just sufficient to avoid dust and dirt 
being swept into it. Where the current of air leaving 
the inlet register is liable to be centered in one point 
in the room it is well to put a diflfusing register on the 
air inlet so that the air will be distributed in a number 




]/WUUWI»in>llfJI,i,UI/ll/lJJl,,,,,,,,,,,,,,,n,..,,,.,,,.,,,.,,,ijj,ji.j,....,,,j,,,n,,,,,,..,,^ 



WilH/itJNUti 



Fig. 59. 

of streams in different directons throughout the room. 
This arrangement of inlet and outlet registers is the 
usual one for school buildings. It is preferable to have 
the inlet and outlet register on the inside walls opposite 
the window surfaces and both registers on the same 
wall. This, however, is not absolutely necessary. The 
inlet and outlet registers should never be on the outside 
walls. Where the inlet register is placed, on the floor 

J50 



Notes on Heating and Ventilation 

and the outlet register at the ceiling then the air com- 
ing from the inlet register will pass directly to the 
outlet register and a large proportion of the heated air 
be lost ; in addition there will be very little circulation 
of air in the room, as shown in Fig. 58. 

In rooms for restaurant purposes, where smoking is 
allowed or in smoking rooms or in kitchens, the air 
must be taken ofif the ceiling, as, the foul air, being 
warmer, rises to the ceiling. In this case it is necessary 
to bring the ventilating air in at the baseboard, at a 
very low velocity and at a number of places and take the 
air out at definite points near the ceiling, as shown in 
Fig. 59. In theaters and churches special means must 
be employed for securing ventilation. It is customary 
to admit the air in a large number of places. Some- 
times this is done by means of a large number of small 
registers placed directly under the seats. Care, how- 
ever, must be used in doing this to avoid drafts. An- 
other method is to employ a large number of openings 
around the sides of the room. The air is usually taken 
oflf near the stage at the lowest point in the auditorium. 
There should be provided in all auditoriums some means 
of taking the air ofif the ceiling, as oftentimes the heat 
given ofif by the occupants of the room is more than 
sufficient to heat the room, and in addition we have the 
heat given ofif by the sources of illumination. This heat 
can be best taken care of at the ceiling line, which is 
naturally the warmest point in the room. 



151 



CHAPTER X. 

DESIGN OF HOT AIR HEATING SYSTEM. 

Design of Hot Air System. — In a hot air furnace 
the cold air from the outside is passed over heated iron 
surfaces, usually enclosed in galvanized iron or brick 
walls. The space between the walls and hot surfaces 
of the furnace is connected to the outside air at the 
bottom and at the top. to the flues leading to the rooms. 
The amount of air circulating through the furnace will 
depend upon the temperature of the hot air leaving the 
furnace and the height and resistance of the flues. In 
order that the air in a room may be quickly replaced by 
warm air it is necessary that the room be provided with 
a foul air flue. 

A great many of the difficulties that have been expe- 
rienced with the hot air system as ordinarily installed 
are due to the sharp competition in business, which has 
resulted in the erection of plants of inferior workman- 
ship and design. One of the commonest mistakes is 
the installation of a furnace much too small to do the 
work properly. The result of putting in a small fur- 
nace is that the fire must be continually crowded so that 
the heating surface is at high temperature and a large 
amount of the heat of the coal is wasted in excessive 
stack temperature. 

The hot air system with natural draft should not be 
used in houses where the horizontal portion of the hot 
air flues would exceed 20 feet in length. In very large 
houses two or more furnaces may be used to avoid 
excessive pipe resistance. 



152 



Notes on Heating and Ventilation 

Hot Air Furnaces. — Hot air furnaces are as varied 
in types as are steam boilers. They are made either 
of cast iron or steel. It is difficult to decide between 
the merits of these two materials. Cast iron is less lia- 
ble to be rapidly deteriorated by rust when the boiler 
stands in the summer, but it is more easily broken either 
by misuse or shrinkage strains in the castings. There 
is no essential difference between the metals in their 
conducting capacity as applied in these furnaces. 

It is very important to see that the furnace is so con- 
structed that the joints between the fire-box and hot-air 
chamber are tight, so that the air entering the rooms 
may not be mixed with gases of combustion. This is one 
of the most difficult things to prevent in the hot air 
furnace. Joints should be as few as possible and ver- 
tical joints should be avoided. The introduction of mois- 
ture into the air passing through the furnace is an im- 
portant consideration and will be treated in a separate 
paragraph. 

The builders rate their furnaces at about their maxi- 
mum capacity-. The rating being expressed as the num- 
ber of cubic feet of building volume the furnace will 
heat. In selecting a furnace it is wise to have 25 to 50 
per cent excess capacity in the furnace over the build- 
er's rating. 

The fire pot of a furnace should be slightly conical 
in shape and should be large enough to contain sufficient 
fuel to last eight hours. The rate of combustion on the 
grate should be taken at not to exceed 4 pounds of coal 
per hour. A high temperature of combustion is usually 
desirable for the best economy, but the stack gases should 
not exceed 500°. 

The air space between the furnace and the outside 

153 



Notes on Heating and Ventilation 

casing should have at least 25 per cent more cross- 
sectional area than the leader pipes taken from it. A 
furnace should be proportioned so that the air leaving it 
should not exceed 180° in temperature. 

There should be one square foot of grate for every 30 
to 50 square feet of heating surface in the furnace. Each 
square foot of heating surface may be assumed to give 
off 1,000 to 1,500 B. t. u. per hour. 

A furnace should be provided with some form of 
shaking and dumping grate which is easily cleaned. In 
addition to draft doors admitting air below the grates, 
the furnace is usually provided with a check damper 
in the smoke pipe. The draft door and check damper 
are arranged so that they may be controlled by chains 
situated in some convenient point in the room above. 

Necessity of Supplying Moisture to Heated Air. — 

It is very important that air after being heated by the 
furnace pass over the surface of a pan of water so that 
it can take up moisture. One pound of air at 32° F. 
will hold in the form of a vapor .003 of a pound of 
water, and at 150 degrees it will hold .22, or about 70 
times as much. If then we take air saturated with 
moisture at an outside temperature of 32 degrees and 
heat it up to 150 degrees we have increased its capacity 
for moisture 70 times. On entering the rooms if the 
air has not been given opportunity to take up moisture 
it will take it up from the objects of the room. This 
drying effect of the air injures the furniture and wood- 
work and affects the persons occupying the room, pro- 
ducing a dry throat and a feeling of cold due to rapid 
evaporation from the skin. 

The usual method of overcoming this is to have a pan 

154 



Notes on Heating and Ventilation 

filled with water situated in the furnace near the fire- 
box. This, however, is the wrong end of the furnace 
to place the pan, as the air entering is coolest at this 
point. The water should be added to the air as it leaves 
the furnace. In some hot air installations every pipe 
leaving the furnace has a trough in it, which is filled 
with water, and from this water the air takes up its 
moisture. 

Cold Air Duct. — The cold air supplied to the fur- 
nace is usually taken from one of the basement win- 
dows and brought to the furnace through a tile or 
wooden duct lined with galvanized iron ; where a tile 
duct is used it is placed below the level of the cellar 
floor. The cold air should be taken from the side of 
the house that is subject to the prevailing winds. It is 
sometimes desirable to have cold air ducts leading to 
different sides of the house, so that the supply of cold 
air may be taken from the windiest side. The cross- 
section of the cold air duct should be 80 per cent of the 
area of the hot air leaders leaving the furnace. 

It is well to provide some means of recirculation of 
the air in the house through the furnace. The air for 
recirculation is usually taken from the Hall. If it is 
desired to recirculate partially and take the balance of 
the air from outside, the recirculating pipe should be 
brought to the furnace separately, and a deflecting plate 
placed in the air space under the furnace. If this is not 
done the air will come in from the outside and may pass 
up the recirculating pipe instead of going to the furnace. 
If, however, the recirculating pipe is only to be used 
when the cold air pipe from outside is closed, then the 
recirculating pipe can be conducted into the cold air 

155 



Notes on Heating and Ventilation 

pipe directly. In this case the cold air pipe and recircu- 
lating pipe must both be provided with dampers. The 
cold air pipe should have at least three-fourths of the 
combined areas of the hot air pipes. 

It is a common error to make the recirculating pipe of 

a furnace system too small. The recirculating pipe 

-should be not less than three-fourths the area of the 

cold air pipe. It is better to have it equal in area 

to the cold air pipe. 

Hot Air Leaders and Flues. — The furnace should 
be centrally located, or if the coldest winds come from 
a certain direction, it can be located more on that side 
of the house from which the cold winds come. The hot 
air flues leading from the furnace should be as short 
and direct as possible ; long horizontal pipes should be 
avoided. Horizontal pipes should pitch sharply towards 
the furnace, three-quarter inch to the foot is good prac- 
tice. All hot air pipes should have nearly equal resist- 
ance to the passage of the air. The hot air flues should 
have as few and as easy turns as possible. They should 
never be placed in the outside walls. Uptake flues of 
any kind in outside walls seldom draw satisfactorily. 
The hot air flue should enter the room in most cases 
opposite the largest exposed glass surface or some dis- 
tance from it. The circulation of air in the room would 
be best if the hot air entered near the ceiling. The prin- 
cipal objection to this is that the register in the wall 
is apt to blacken the wall and it does not allow people 
to warm themselves over it. Floor registers are very 
objectionable as they always serve as receptacles for all 
kinds of rubbish and sweepings. 

Dampers should be provided in all pipes leading to 

156 



Notes on Heating and Ventilation 

rooms above the first floor. If all the registers are pro- 
vided with dampers there is danger of burning the fur- 
nace, due to shutting off all the passages for removing 
hot air and preventing circulation in the furnace. It is 
good practice to have no valve in the hall register so one 
pipe will always be open. 

Proportions of Hot Air Flues. — The velocity of air 
for first floor leaders may be calculated as three or 
four feet per second, second floor four to five feet per 
second, third floor and floors above five to six feet per 
second. The flues leading to the second and third floor 
room may have a velocity as high as 400 feet per minute. 

In the best installations the leads and flues are double 
walled with asbestos between the walls. The cross- 
sectional area of all the leaders should be from 1.1 to 1.5 
times the area of the grate. 

The registers should be proportioned so as to give 
a velocity of two to three feet per second on the first 
floor and three to four feet per second on the floors 
above. The effective area of the ordinary registers is 
about 50 per cent of the actual area, taking outside di- 
mensions. 

H. B. Carpenter, in a paper before the Society of 
Heating and Ventilating Engineers (Transactions, vol. 5, 
p. 77), gives the following rule for finding the cubic 
feet of air passing through pipes per minute : 

To the first floor multiply the area in inches by 1.25. 

To the second floor multiply the area in inches by 1.66. 

To the third floor multiply the area in inches by 2.08. 

It is good practice to figure on changing the air in the 
principal rooms five times per hour in hot air heating. 

Foul Air Flues. — The foul air flues should be placed 

157 



Notes on Heating and Ventilation 

in the inside walls and with foul air registers at the 
baseboard. The reason being that the hot air entering 
the room opposite the window surfaces rises to the 
ceihng, passes along the ceiling to the windows and is 
cooled. It then drops to the floor line, passes along 
the floor and out the foul air register. The hot air reg- 
ister should be a sufficient distance from the foul 
air register so that the hot air will not pass directly to 
the foul air flue. A cheap foul air flue can be made by 
having a register in the baseboard opening into the 
spaces between the studs, selecting a space that is open 
to the attic, a ventilator is placed on the attic space and 
discharges foul air out of doors. No two rooms should 
open into the same studding space. A still better draft 
can be produced by extending each flue separately by 
galvanized iron pipe to the ventilator. If no ventilating 
flues are provided, it is very difficult, especially if the 
house is tight, to get a proper circulation of hot air from 
the furnace; you cannot put hot air into a room if 
there is no provision for taking cold air out. 

The area of these foul air flues should be not less 
than 80 per cent of that of the warm air flues and they 
are often made equal in area to the area of the warm 
air flues. 

A fireplace makes one of~ the best forms of foul air 
flue. In a house well provided with fireplaces, it is 
often not necessary to provide any other foul air flues. 

General Proportions of Hot Air Systems. — The size 
of the hot air flue, vent flue, hot air register, heating 
surface and grate surface in the furnace is given in 
Table XLI. This table is given for rooms of average 
proportion and under average conditions. 

168 



Notes on Heating and Ventilation 

TABLE XLIII.— PROPORTIONS OF HOT AIR HEATING SYSTEM. 

Contents of Room in Cubic Feet. 500 1,000 1,500 
First Floor — 

Diameter hot air flue, In 6 8 9 

Diameter foul air flue, in 6 8 9 

Second Floor — 

Diameter hot air flue, in 6 7 8 

Diameter foul air flue, in 6 7 8 

Grate area in furnace, sq. in 25 50 76 

Heating surface in furnace, sq. ft 5 10 15 

2,000 . 2,500 3,000 3,500 4,000 5,000 6,000 8,000 10,000 

10 ' 11 12 13 14 16 17 20 24 

10 11 12 13 14 16 17 20 24 

9 10 11 11 12 14 15 18 20 

8 ■ 9 9 10 10 12 12 14 16 

100 125 150 175 200 250 300 350 40U 

20 25 30 35 40 50 62.5 SO 100 

The following assumptions have been made the above 
table : Temperature outside air, degree ; temperature 
of air in the room, 70 degrees ; changes of air in the 
room, three times per hour. 

Velocity of air in hot air flues, 1st floor, 3 ft. per 
second. 

Velocity of air in hot air flues, 2nd floor, 4 ft. per 
second. 

Velocity of air in four air flues, 1st and 2nd floors, 3 ft. 
per second. 

Temperature of air entering the room, 160 degrees. 

Proportion of grate surface to heating surface, 1 to 30. 

Pounds of coal burned per square foot of grate sur- 
face per hour, 3. 

Suggestions for Operating Hot Air Furnaces. — The 

temperature of the rooms should be regulated by the 
drafts of the furnace as much as possible. The heating 
surfaces of the furnace should never be brought to a 
red heat. If it is necessary to do this to keep the rooms 
warm, the furnace is too small. 

Ashes should be frequently removed from the furnace, 
as an accumulation of ashes may burn out the grate. 
Never shake the fire more than is necessary to expose 

159 



Notes on Heating and Ventilation 

the red coals to the ash pit. The furnace should be 
cleaned at least once a year. The water pan of the fur- 
nace should be kept full of water, 

ROUGH RULES FOR HOT AIR SYSTEM. 

1. The volume of the house divided by 50 equals 
square feet of heating surface in furnace radiator. 

2. The volume of the house divided by 20 equals 
the number of square inches of grate area in the furnace. 

3. Divide the volume of the room by 20 and the 
square root of the quotient will be the diameter of the 
furnace pipe for the first floor room. For second floor 
rooms divide the volume by 25 and the square root of the 
quotient will be the diameter of the furnace pipe. 

Example of Hot Air System. — As an example of 
the hot air system applied to the ordinary dwelling, take 
the same house that was used as an example of direct 
steam heating. The heat lost from the rooms would be 
the same as in the case of direct steam. As an example 
of an individual room take the parlor. 

From Table XX we see that the volume of the parlor 
is 1,665 cubic feet and the heat lost 10,395 B. t. u. 
per hour. In figuring the heating system for the parlor 
the following assumption will be made : The hot air 
enters the room at 160°. Cold air enters the furnace 
at 0°. The temperature in the room is 70°. Then the ^ 

air entering the room i^s reduced in temperature 160— ^g;>I^ 
70=90°. Each pound^of air on having its temperature 
reduced 90° would give up .2375X90=21.4 B. t. u. 
Then there will have to be introduced into the room to 
supply heat lost from the room 10,395-1-21.4=485 pounds 
of air per hour. At atmospheric pressure a pound of 

160 



Notes on Heating and Ventilation 

air occupies approximately 13 cubic feet, hence 485 
pounds of air is equal to 6,300 cubic feet. This is the 
amount of air which must be deHvered to the room per 
hour; 6,300 cubic feet of air per hour is equal to 1.75 
cubic feet per second. Allowing a velocity of 3 feet per 
second, the area of the pipe would be 1.75^3 = . 58 square 
feet, which is equivalent to 84 square inches, or approxi- 
mately the area of a pipe 10.5 inches in diameter. To 
warm the air going- to the parlor would require 485 X 
.2375X160=:18,500 B. t. u. In a similar way the same 
quantities have been calculated for the other rooms. 
Except that for the second floor room, a velocity of 4 feet 
per second has been allowed. 

TABLE XLIV. 

B.t.u. Cu. ft. Diam- 

Volume lost. B.t.u. of air eter 

of from room given air entering of hot 

room, per hour, per hour. room, air pipe. 
First Floor. 

Parlor 1,665 10,305 18,500 6,300 lOVo 

Sitting room 2,100 7,035 12,500 4,350 9" 

Dining room 1,640 7,350 12,800 4.500 9 

Kitchen 1,610 10,300 18,000 6,250 IOV2 

Hall 1,210 7,035 12,500 4,350 9 

Second Floor. 

West Alcove 1,320 10,050 17,900 6,200 9 

Alcove 810 7,560 13,400 4,750 8 

South chamber 1,560 7,035 12,500 4,400 8 

North chamber 1,440 7,455 13,300 4,650 8 

Bath 410 3,150 5,600 1,850 G 

East chamber 880 5,250 • 9,400 3,300 7 

Halls 88 2.730 4,800 1,750 6 

151.200 

Column 3 of Table XLIV shows the heat which is left 
by the air in the room. Column 4 .shows the heat used 
to warm the air entering the room. The difference be- 
tween these two columns is the heat lost up the ventilat- 
ing flues. This loss should not be charged against the 
hot air furnace, but should be considered as the loss 
that must be charged to ventilation. The loss is about 
44 per cent if the temperature of the outside air is at 0° 

161 



Notes 



o n 



Heating 



and 



Ventilation 



and the temperature of the air entering the room is 160°. 
As the temperature of the outside air or the incoming 
air is increased proportionately more heat enters the 
room and this loss becomes less. During the average 
winter weather the outside air is 35°, in which case the 
per cent of loss by ventilation, that is, through the ven- 
tilating flues, is about 30 per cent. 




Fig. 60. 



Summing up column 4 of the table gives the heat 
required to warm the air entering the entire house in 
zero weather or 151,200 B. t. u. If we assume that 80 



162 



Notes on Heating and Ventilation 

per cent of the coal goes into the heated air, then there 
will be required from the coal 151,200-^.8=188,500 
B. t. u. per hour. A good anthracite coal contains about 
13,500 B. t. u. ; then in zero weather this house 
would use 188, 500-f-13, 500=14 pounds of coal per hour. 
As the average loss from a house during the heating 
season is approximately 50 per cent of the loss during 
zero weather, the average consumption of coal in this 
house for the heating season would be 14X -5=7.00 
pounds of coal per hour. Assuming the furnace to be 
operated 24 hours per day and 200 days per year, the 
coal consumption for this house would be 7 X 24X200 -f- 
2,000=16.8 tons. Fig. 60 shows a cross section of a 
house with the hot air system installed. 



163 



CHAPTER XI. 

FAN SYSTEM OF HEATING. 

Where it is necessary to introduce large quantities 
of air into a building for the purpose of ventilation a 
natural system of circulation is out of the question and 
it is necessary to force the air into the building by some 
mechanical device. This is usually done by means of a 
steel plate blower which delivers the air with sufficient 
pressure to force the air into all rooms in the building. 
The pressure required in the average building does not 
usually exceed one-quarter ounce. -The mechanical sys- 
tem of ventilation has the additional advantage that its 
operation is entirely independent of the heating of the 
building and the building may be ventilated as easily in 
the summer as in the winter. The natural system of 
ventilation depends entirely upon the air in the flues 
being heated, and during the summer periods the system 
is inoperative. 

Systems of Fan Heating. — There are two general 
schemes of fan heating, one in which the air is heated 
to a temperature higher than that in the room, so that 
it furnishes enough heat to supply the heat lost from the 
walls and windows, as well as to furnish air for ventila- 
tion. In the other system the heat loss from walls and 
windows is supplied by direct radiation situated in the 
room and the fan supplies only the necessary amount 
of air for ventilation. In the latter system the air for 
ventilation is supplied at about the temperature to be 
maintained in the room. The first system, in which all 
the heat is supplied by means of a fan, is most applica- 

164 



Notes on Heating and Ventilation 

ble in buildings that must be heated and ventilated both 
night and day. Hospitals and asylums are buildings of 
this class. It has certain disadvantages, however. When 
a room has very large glass surfaces it is almost impos- 
sible with this system to prevent strong cold drafts com- 
ing down along the window surfaces. The system is 
in many cases wasteful. In order to heat a building it is 
often necessary to admit more air than is required for 
the purpose of ventilation, and all the heat put into the 
air to raise the temperature of the outside air to the 
temperature of the room is lost. On the other hand, 
this system requires but one system of heating, which 
makes it less expensive to install. 

The second system mentioned, where direct radiation 
and a fan are both used, is most applicable in buildings 
that require ventilation only part of the time. Schools, 
factories, office buildings are buildings that may be in- 
cluded in this class. While the buildings are filled with 
occupants the fan system is operated ; as soon as the 
occupants leave the building the fan system is closed and 
the building kept warm by means of direct radiation. 
The building is thus kept warm at a minimum expendi- 
ture for fuel. There is no necessity of introducing into 
the building more air than is necessary for ventilation. 
But the system is expensive to install, as it involves 
installing two separate systems of heating. This 
system is being more and more favorably considered, 
however, in connection with the class of buildings men- 
tioned. 

General Arrangement of the Fan System. — The us- 
ual arrangement of the fan system is shown in Fig. 61. 
The air is drawn first through a series of tempering coils 

165 



Notes 



o n 



Heating and Ventilation 



shown at A. Then it enters a tempered air chamber 
in which is located the fan. This deHvers the air through 
a series of heating coils B into the hot air chamber. 
From this hot air chamber the individual rooms in the 
buildings take their heat. The tempered coils are usually 
designed to heat the air to about 70°. The fan takes 
this air at 70° and passes it to the heating coils. After 
leaving the heating coils the temperature of the air is 
from 130° to 140°. Where the air is used for ventilation 
only the heating coils are omitted and the air is deliv- 




Fig. 61. 

ered by the fan from the tempered air chamber directly 
to the room. 

Quantity of Air to Be Supplied. — The quantity of 
air to be supplied to each room will depend upon the 
system of heating employed. If the heating is done en- 
tirely by fan enough air must be admitted so that the 
heat left by the air will be sufficient to heat the room. 
In audience and school rooms the amount of air necessary 
to supply proper ventilation is usually sufficient for heat- 
ing. In offices and living rooms more air will have to 

166 



Notes on Heating and Ventilation 

be supplied in order to heat the room than would be 
necessary for purposes of ventilation. Roughly speak- 
ing, if the number of cubic feet of air supplied to the 
room per hour is four times the cubic contents of the 
room the room will be heated, providing the air be sup- 
plied at not less than 140°. In a system where direct 
radiation is used to supply losses from walls and win- 
dows only enough air is introduced to supply the neces- 
sary ventilation. The amount of air necessary can be 
determined by rules previously given under the head of 
Ventilation. 

Size, Speed and Horsepower of Fan. — In most cases 
the type of fan known as the steel plate blower or multi- 
vane fan is best adapted to the w^ork of fan heat- 
ing. The theory of this fan has been discussed by 
Weisbach and Lindner in their treatises, also by vari- 
ous writers in the Transaction of the Society 
of Heating and Ventilating Engineers. The results 
derived are difficult of application. The following 
general statement may be made, however: The dis- 
charge capacity of a fan depends upon the speed of 
the fan tips, the size of the fan blades, and the size of 
the discharge openings. As the discharge opening of 
the fan is decreased the velocity of the air leaving the 
fan increases and the pressure of air in the fan case 
increases until we get to the maximum pressure that 
can be produced by a certain velocity of fan tips. This 
will occur when the area of the outlet equals the effec- 
tive area of the fan blades. This is the point at which 
the fan delivers the maximum amount of air correspond- 
ing to the pressure for a given speed. If we further 
reduce this discharge outlet the pressure in the fan case 

167 



Notes 



o n 



Heating and Ventilation 



remains constant, the quantity of air discharged is re- 
duced and the power to drive the fan is reduced. 

TABLE XLV.— FAN CAPACITIES. 

Speeds, Capacities and Horse Powers of "A B C" Steel Plate Fans 

of "Varying Revolutions. 



R.P.M. 


FAN 


BO 


60 


70 


80 


90 


100 


110 


120 


140 


leo 180 


200 

3141 


280 


240 




PerV. 


785 


942 


1100 


1257 


1414 


1571 


1728 


1885 


2200 


2513 


2837 


3455 


3769 




AirV. 


685 


m) 


957 


1092 


12iW 


1867 


1503 


1640 


l."15 


2182 


2459 


2732 


8005 


3279 


100 


Pres. 


.017 


.025 


.034 


.044 


.055 


.068 


.082 


.1(K) 


.134 


.175 


.231 


,273 


.385 


.401 




Cu. Ft. 


682 


1121 


1870 


2652 


3840 


5475 


6395 


9.565 


14916 


21750 


S0221 


4^608 


55201 


71941 




H. P. 


.160 


;222 


.370 


.476 


.672 


1.01 


1.37 


2.03 


3.46 


5.47 


7.7 


12.0 


17.1 


25.1 




PerV. 


981 


1178 


1375 


1571 


1768 


1964 


2160 


2356 


2750 


8141 


3533 


39?fl 


4318 


4711 




AirV. 


853 


1025 


11P6 


1366 


1.538 


1707 


1879 


2029 2390 


2724 


3078 


8415 


8756 


4098 


125 


Pres. 


.027 


.089 


.053 


.060 


.089 


lOH 


.132 


.153 


.212 


.276 


.350 


.435 


.525 


.626 




C«. Ft. 


852 


1402 


2338 


31.58 


4809 


6844 


7992 


11945 


18645 


27170 


37767 


5?010 


68997 


99910 




H. P. 


.175 


.284 


.439 


.5S8 


.934 


1.34 


2.06 


2.90 


5.00 


8.15 


12.5 


19.3 


29.2 


435 




PerV. 


1177 


1413 


1650 


1886 


2121 


2356 


2592 


2827 


3S00 


3770 


4240 


4711 


5182 


5653 




Air V. 


1025 


1230 


1432 


1640 


1845 


2044 


2255 


2460 


2870 


3280 


3688 


4098. 


4500 


4928 


150 


Pres. 


.039 


.056 


.075 


.100 


.1?0 


160 


190 


.230 


.800 


.400 


.503 


626 


758 


.904 




Cu. Ft. 


1023 


1681 


2805 


3979 


5760 


8110 


(BM> 


14360 


22374 


32610 


45325 


62412 


82811 


10812C 




H. P. 


.200 


-325 


.531 


.756 


1.27 


1.86 


2.7* 


3.10 


7.22 


11.3 


19.6 


32,1 


46.2 


68.6 




PerV. 


1874 


1649 


1925 


2200 


2474 


2749 


3024 


■3297 


3850 


438Q 


4947 


5496 


6046 


6596 




AirV. 


1195 


1434 


1674 


1914 


2152 


2390 


2630 


2868 


8350 


3826 


4303 


4781 


5?fiO 


574? 


175 


Pres 


,053 


.076 


.101 


.134 


.172 


.212 


.2.58 


.WW 


.420 


.554 


687 


84^ 


U02 


1.21 




Cu Ft. 


1194 


1962 


3274 


4622 


6729 


9594 


11200 


16715 


26100 


88043 


52888 


72814 


96626 


126089 




H.'P. 


.225 


.393 


.647 


1.01 


1.74 


2.46 


3.55 


5.52 


9.91 


17.3 


27.9 


44.2 


67.1 


103.0 




Per V. 


1570 


1884 


2200 


2511 


2828 


8142 


3456 


8770 


4400 


5026 


5654 


6282 


6910 


7538 


— 


AirV. 


1366 


1640 


1915 


2187 


2460 


2737 


■mn 


3280 


38.'^0 


♦375 


4918 


5465 


6011 


6558 


200 


Pres. 


.069 


.101 


.184 


.175 


.225 


274 


.338 


.392 


.537 


.700 


.503 


1.12 


1.34 


a59 




Cu. Ft. 


1364 


2242 


3740 


5304 


7690 


10960 


128.S0 


19150 


29850 


43520 


60442 


83331 


110422 


148902 




H. P. 


.262 


.478 


.855 


1.26 


2.05 


3.16 


4.69 


7.01 


13.3 


23.7 


39.2 


62.1 


96.6 


154.5 




PerV. 


1766 


2120 


2475 


2829 


8182 


3534 


3888 


4241 


4950 


56.54 


6360 


7065 


7774 






AirV. 


1536 


1844 


2153 


2459 


2767 


8073 


3383 


36SH 


mf, 


4919 


5583 


6148 


6762 




225 


Pres. 


.0S7 


.126 


,172 


.225 


.285 


.351 


.421. 


.507 


.690 


.601 


1 14 


1.41 


1.69 






Cu. Ft. 


1534 


2523 


4207 


5968 


8655 


12334 


14385 


21500 


;«560 


48680 


68000 


93634 


124217 






H. P. 


.300 


.581 


1.08 


1.57 


2.61 


4.09 


5.95 


9.29 


17.0 


31.1 


52.8 


87.9 


142.5 






PerV. 


1963 


2355 


2750 


3143 


3535 


8927 


4320 


4712 


5500 


6283 


7067 


7852 








Air V. 


1708 


2048 


2392 


2784 


wno 


3416 


3758 


4100 


4780 


5450 


61 4M 


6840 




250 


Pres. 


.109 


.056 


.213 


.280 


.3fl(> 


430 


.520 


.630 


.860 


I 12 


1.48 


1.73 






Cu. Ft. 


1706 


2793 


4675 


6332 


Hfi(X) 


13705 


16000 


23950 


37310 


54200 


75558 


104036 






H. P. 


.375 


.684 


1.22 


1.79 


8.32 


4.97 


7« 


116 


^2.5 


41.2 


71.7 


121.4 






PerV. 


2159 


2591 


3025 


3457 


8889 


4319 


4731 


5183 


6050 


6911 


7774 








AirV. 


1878 


2258 


2632 


3008 


3388 


3755 


40tO 


4507 


5263 


6013 


6768 




875 


Pres. 


.131 


.189 


,25H 


.337 


426 


.5V6 


.623 


.7.56 


1.04 


1.35 


1 71 






Cu. Ft. 


1876 


3083 


5142 


7294 


10578 


15773 


17394 


26278 


41020 


.5K328 


88104 






H. P. 


.436 


.821 


1.45 


2.35 


3.92 


6.oa 


909 


14.5 


29.4 


54.7 


89.3 






PerV. 


2355 


2826 


3300 


3771 


4242 


4712 


5184 


5654 


6600 


7539 








AirV. 


2050 


24.58 


2H75 


3280 


3685 


41(NI 


4510 


49£0 


5745 


6555 




300 


Pres. 


:160 


.225 


mi 


.401 


520 


.630 


.760 


.910 


15'6 


1.62 






Cu. Ft. 


2016 


3363 


5610 


7957 


11520 


16i5<) 


19200 


28800 


44750 


63629 






H.P. 


.500 


.975 


1.73 


2.86 


4.63 


7.U 


11.4 


18.1 


87.5 


69.3 






Per V. 


2747 


3297 


3850 


4399 


4949 


'^^ 


6018 


6.597 


7700 








AirV. 


2390 


2863 


3345 


3827 


4-295 


5262 


5724 


6680 


NOTE 


350 


Pres. 


.216 


.306 


41 H 


.550 


.693 


.8.50 


.970 


1.25 


1.68 


These 6gures guarantee<i to 




Cu Ft. 


2387 


8928 


6545 


9282 


13410 


19110 


22:«t5 


33400 


52206 




H. P 


.663 


1.28 


2.38 


8.89 


6.65 


107 


17 2 


28.3 


55.8 


be correct with the resistance 




PerV. 


3140 


3768 


4400 


5028 


56.56 


6282 


691 ;' 


7540 




ordinarily found in heating 




AirV. 


2732 


3278 


3830 


4374 


4926 


5470 


6013 


6560 


work. 


4C0 


Pres. 


.277 


.399 


.546 


.713 


904 


1.14 


1.42 


163 






Cu. Ft. 


2729 


4384 


7480 


10620 


15400 


21950 


25574 


38300 






HP, 


.7.50 


170 


3 19 


5.04 


9^4 


15.3 


25.2 


39 2 





The theoretical relations connecting the pressure of 
the air, the quantity of air delivered, power to drive the 
fan and the speed can be stated briefly as follows : The 
quantity of air delivered is proportional to the peri- 
pheral velocity of the fan tips and to the width of the 

3 68 



Notes 



o n 



Heating and Ventilation 



fan tips. The pressure produced is proportional to the 
square of the peripheral velocity of the fan tips and 
the power necessary is proportional to the cube of the 
peripheral velocity of the fan tips and to the quantity 

TABLE XLVI. — FAN EFFICIENCY I'NDER VARYING PRES- 
SURES. 

Sreeds, Capacities and Horse Powers of "A B C" Steel Plate Fans 
of Varying Pressures. 



PRESSUKES. 


Hoi. 


Hoi. 


Koi. 


1 Ol. 


l>i 01. 


1% 01. 


IK 01. 


2 01. 


2 "4 01. 


8 01. 


60 


CU. FT. 

R P. M. 

H. P. 


2740 
380 
.80 


3900 
.540 
1.60 


4760 
6.59 
2.66 


5490 
760 
385 


6090 
847 
5 32 


6700 
930 
6.65 


73.50 
1004 
8.22 


7750 
1075 
10.25 


8650 
1200 
14.38 


9520 
1320 

18.85 


60 


CU. FT 

R. P. M. 

H. P. 


3,i.T0 
317 
1.03 


5040 
449 
2.05 


5490 
549 
3.42 


7100 
633 
4.95 


7910 
706 
6.84 


8700 
776 
8.54 


9410 

838 

10.60 


10200 
895 
13.2 


11210 
1000 
18.45 


12330 
1100 
24.3 


70 


CU. FT. 

R. P. M. 

H. P. 


5220 
271 
1.51 


7350 
383 
3.02 


9050 
471 
5.04 


10400 
.542 
7.30 


11600 

605 

10.10 


12700 

663 

12Si; 


13750 

716 

1560 


147.50 

768 

19.40 


16.500 

857 

27. '20 


18000 
938 
35.7 


80 


CU. FT. 

R. P M. 

H. P. 


630 
238 
1.82 


8900 
836 
3.65 


10940 
412 
6.08 


125.50 
474 

8.82 


14000 

5.30 

12.15 


153,50 

580 

15.20 


16600 
627 

18.85 


17300 

672 

23.40 


198S0 

750 

S3.80 


21920 
825 
43.2 


90 


CU. FT. 

R. P. M. 

H. P. 


7850 
211 
2.27 


11050 
299 
4.53 


13600 
366 
7.56 


15600 

421 

1100 


17450 

470 

15.10 


19100 

515 

18.90 


20650 

557 

23.40 


22100 

5<:6 

29.10 


•247.50 

666 

40.70 


27300 
734 
53.5 


100 


CU. FT. 

R. P. M. 

H. P. 


9.>t0 
1«0 
2.76 


13.500 
268 
5.,52 


16.500 
329 

9.a) 


19050 

380 

13.35 


21300 

424 

18.42 


23300 

464 

23.00 


2.5200 

502 

28.60 


•27000 
.537 

ss.to 


30.^00 

600 

49.60 


33000 
659 
65.2 


110 


CU. Ft. 

R. P. M. 

H. P. 


11870 
173 
8.43 


16700 
244 
6.85 


20600 

800 

1144 


23600 

345 

16.60 


26400 

885 

22.W) 


28900 

422 

28.60 


31.300 

4:)6 

35.50 


33500 

488 

44.00 


37.500 
546 
61.7 


41200 
600 
81.2 


]20 


CU. FT. 

R. P. M. 

H. P. 


15030 
1.59 
4.32 


21000 
224 
8.65 


2.5840 

274 

14.40 


29700 

816 

20.60 


33200 

3.54 

28.80 


36400 

387 

36.00 


39400 

418 

44.60 


42^200 

448 

55.45 


47100 
500 
777 


51800 

550 

102.1 


140 


CU. FT. 

R. P. M. 

H. P. 


19800 
136 
5.72 


27900 

192 

11.42 


84200 

2:{5 

19.00 


39400 

271 

27.60 


44000 

302 

38.10 


48200 

331 

47.60 


51200 

357 

59.00 


55800 

883 

73.30 


639C0 

439 

1027 


68400 

470 

135.5 


160 


CU. FT. 

R. P M 

H. P 


.2.50:>0 

118 
7.29 


85600 

168 

14.60 


4;i700 

206 

24.32 


502.50 

237 

35.20 


56150 

265 

48.60 


61.500 

290 

160.75 


66500 

814 

75.30 


712.50 

336 

93.50 


79200 

373 

134.0 


87500 

412 

172.0 


180 


CU. FT. 

R. P. M. 

H. P. 


S1410 
106 
9.07 


44200 

149 

18.13 


54300 

183 

30.24 


62700 

211 

43.80 


69700 

235 

60.48 


76700 
259 
75.5 


82700 
279 
93.6 


88400 

•298 

116.^20 


99000 

834 

131.0 


108400 

866 

214.0 


200 


CU. KT. 

R. P. M. 

H. P 


38000 

95 

1102 


53700 

134 

22.20 


66000 

165 

.36.80 


75700 
189 
53.8 


84950 
212 
73.5 


93000 
2:12 
920 


100500 

•251 

1140 


107:00 

268 

1415 


r20000 

300 
1985 


134000 

830 

261.0 


220 


CU. FT. 

R. P. M. 

H. P. 


46S0O 

87 

13.48 


66300 

123 

27.00 


80900 

150 

44.90 


93200 

173 

65.10 


104000 
193 
89.6 


113.500 

211 

112.0 


123300 

•229 

139.0 


131400 

244 

178.0 


147100 

274 

243.0 


161500 

300 

818.0 


240 


CU. FT. 

R. P M. 

H P. 


56400 

80 

1610 


79000 

112 

32.30 


96.-)00 

137 

53. M) 


11-2000 

1.59 

7.H,00 


124800 

177 

107 4 


136800 

194 

1340 


147400 

209 

106 


1.5S0OO 

•224 

206.0 


176100 194000 

2.50 275 

2«0.0 3820 



of ai * delivered. Mr. M. C. Huyett gives the follow- 
ing approximate rule for finding the capacity of a fan : 
The quantity of air in cubic feet delivered per revolu- 
tion is equal to one-third the diameter of the fan 
wheel multiplied by the width of the blades at cir- 

169 



Notes on Heating and Ventilation 

cumference, multiplied by the circumference of the fan 
wheel. All dimensions expressed in feet. 

Professor R. C. Carpenter gives the following rule 
for determining the horsepower required by the fan : 
The horsepower required for the fan is equal to the 
fifth power of the diameter of the fan wheel in feet 
multiplied by the number of revolutions per second, 
divided by 1,000,000 and multiplied by one of the fol- 
lowing coefficients — for free delivery, 30 ; for delivery 
against 1-ounce pressure, 20 ; for delivery against 2 
ounces pressure, 10. The best method of obtaining the 
horsepower to drive a fan and the capacity of the fan 
is by reference to the table. 

Table XLV gives the speed, capacity and horsepower 
required for various sized fans as determined by the 
American Blower Co. 

Table XLVI gives similar results for different sized 
fans at varying pressure. 

Table XLVII gives the results for a fan of the multi 
vane type, such as the Sirocco. 

The table should be made use of in the following 
manner: Having determined the quantity of air re- 
quired for the entire building, we select from the table 
a fan which would give the proper capacity. In doing 
this three things must be considered. The fan must 
have sufficient capacity to deliver the amount of air 
required. It must deliver this air with the minimum 
horsepower, and it must rotate with sufficient speed to 
product a pressure in the fan system sufficient to over- 
come the resistance of the piping. It is always possi- 
ble to select either a small fan driven at a high speed or 
a large fan driven at a low speed, both of which will 
deliver the same capacity of air. A large fan may be 

170 



Notes 



o n 



Heating and Ventilation 



TABLE XLVII. 

Speeds, Capacities and Horse Powers of Single Inlet, Standard 
Width Fans at Various Pressures. 



Fisura Giren Retiteaeat Dnumie Prritura in Ounco per Square Inch. Foe Slabc Piewire Deduct 26.9%. 
For Velodly Pienure Deduct 71.2%. 



No. 
o( 


Uumeter 
Wheel 




to.. 


10.. 


10.. 


10.. 


uo.. 


li Ol. 


UO.. 


2 0.. 


210.. 


3 0.. 


M 


3 


CU. FT. 
R.P. M. 
B. H. P. 


38 
2290 
.005 


55 
3230 
013 


67 
3960 
024 


77 
4580 
037 


87 
5120 
051 


95 
5600 
068 


102 
6050 
085 


110 

6460 

105 


122 

7232 

145 


135 

7920 
190 




4i 


CU. FT. 
R.P. M. 
B. H. P. 


87 
1524 
Oil 


125 
2152 
030 


152 
2640 
053 


175 
3048 
084 


197 
3400 
.116 


215 
3732 
.153 


232 

4OJ0 

193 


250 
4304 
.238 


277 
4816 
.330 


;«.5 

5280 
433 




• 


CU. FT. 
R.P. M. 
B. H. P. 


155 
1U5 

.0185 


220 
1615 
052 


270 
1980 
095 


310 
2290 
.147 


350 
2560 
205 


380 
2800 
.270 


410 

3025 

.34 


440 

3230 

.42 


490 
3616 

.58 


540 

3960 

76 




n 


CU. FT. 
R.P. M. 
B. HlP. 


242 
915 
029 


344 
1290 
0«2 


422 
1585 
149 


485 
1830 
.230 


548 
2050 
320 


594 
2240 
422 


640 

2420 
532 


688 
2580 
656 


768 
2890 
910 


844 
3170 
1 19 




» 


CU. FT. 
R.P. M. 
B. H. P. 


350 
762 
.042 


500 
1076 

.118 


610 
1320 
.216 


700 
1524 
.333 


790 
1700 
.463 


860 
1866 
.610 


930 
2020 


1000 

2152 

95 


1110 
2408 
1 32 


1220 
2640 
1.73 




12 


CU. FT. 
R.P. M. 
B. H. P. 


625 
572 
.074 


880 
808 
208 


1080 
990 
.381 


1250 
1145 

.588 


1400 
1280 

.82 


15J0 
1400 
1 08 


1650 
1512 
1.36 


1770 
1615 
1 66 


1970 
1808 
2 32 


2170 
1980 
3 05 




IS 


CU. FT. 
R.P. M. 
B. H. P. 


975 
456 
115 


1380 
645 
326 


1690 
790 
.600 


1950 
912 
923 


2180 
1020 
1 29 


2400 
1120 
1.69 


2590 
1210 
2.14 


2760 
1290 
2 61 


3090 
1444 
3 65 


3390 
1580 
4 8 




18 


CU. Fr. 
R.P. M. 
B. H. P. 


1410 
381 
.167 


1990 
538 
470 


2440 
660 

862 


2820 
762 
1.33 


3160 
850 
1.85 


3450 
933 
2 43 


3720 
1010 
3.07 


3980 
1076 
3.75 


4450 
1204 
5 25 


4880 
1320 

6 9 




21 


CU. FT. 
R.P. M. 
B H. P. 


1925 
326 

.227 


2710 
482 
.640 


3310 
565 
1 17 


3850 
652 
1 81 


4290 
730 
2 53 


4700 
800 
3 33 


5070 

864 
4 18 


5420 
924 
5 11 


6060 
1032 
7 15 


6620 
1130 
9 4 




24 


CU. Fr. 

R.P. M. 
B. H. P. 


2500 
286 
.296 


3540 
404 

.832 


4340 
495 
1.53 


5000 
572 
2 35 


5600 
640 
3 28 


6120 
700 

4 :g 


6620 
756 
5 44 


70BO 
807 
6 64 


7900 
904 
9.3 


8680 
990 
12.2 




27 


CU. Fr. 
R.P. M. 
B. H. P. 


3175 
254 
373 


4J90 
359 
1 05 


5500 
440 
1.94 


6350 
508 
2 98 


7100 

568 
4 16 


7780 
622 

5.48 


8400 
672 
6 90 


8980 
718 

8.44 


10050 
804 
11 8 


J 1000 
880 
15 5 




30 


CU. FT 
R.P. M. 
B. H. P. 


3910 
228 
460 


5520 
322 
1 30 


6770 
395 
2 40 


7820 
456 
3 68 


8750 
510 

5 15 


9600 
560 
6 75 


103^ 
604 

8 53 


11050 
645 
10 4 


12350 
722 
14 5 


13550 
790 
19 1 




36 


CU. FT. 
R. P. M. 
B. H. P. 


5650 
190 
66.1 


7950 
269 

1 87 


9750 
330 
3 44 


11300 
381 
5 .30 


12M0 
425 
7 40 


13!>00 
466 
9 72 


14900 

504 

12.26 


15900 
538 
15 


17800 
602 
20 9 


19500 
660 
27 5 




42 


CU. FT. 
R. P. M. 
B. H. P. 


7700 
163 
90? 


10850 
231 
2 55 


13300 
283 
4 69 


15400 
326 
7 24 


17170 
365 
10 1 


18800 
400 
13 3 


20300 
432 
16 7 


21700 
462 
20 4 


24250 
516 

28 5 


26600 
566 
37 5 




4a 


CU. FT 
R. P. .M. 
B. H. P. 


10000 
143 
1 18 


14150 
202 
3 32 


17350 

248 
6 10 


20000 
286 
9 40 


22400 
320 
13 1 


24500 
350 
17 2 


26500 

378 

21 75 


28300 
403 
26 6 


31600 
452 
37.1 


34700 
495 

48 8 




54 


CU. FT. 
R. P. M. 
B H. P. 


12700 
127 
1 49 


17950 

179 

4 20 


22000 
220 
7 75 


25400 
254 
11 9 


28400 
284 
16 6 


31100 
311 
21 9 


33600 
336 
27 6 


35900 
359 
33 7 


40200 
402 
47 1 


44000 
440 
02 




60 


CU. FT. 
R.P. M. 
B H. P. 


15650 
114 

1 84 


22100 

161 

5 20 


27100 

198 

9 58 


31300 
228 
14 7 


35000 
255 
20 6 


38400 
280 

27 


41400 
302 
34 1 


44200 
322 
41 6 


4940O 
361 

.58 2 


51200 
396 
76 5 




66 


CU FT. 
R. P. M. 
B. H. P. 


18950 

104 

2 23 


26800 

147 

6 30 


32850 
180 
11 6 


37900 
208 
17.8 


42300 
232 
24 9 


46400 
254 

32 7 


50100 
275 
41 2 


53600 
294 
50 4 


60000 
328 
70 4 


65700 
360 
92 6 




72 


CU. FT. 
R.P. M. 
B. H. P. 


22600 

95 

2.66 


31800 
134 

7 48 


39000 
165 

13 7 


45200 
190 

21 2 


50600 
212 
29 6 


55200 
233 
38 9 


59600 
252 
49 


63600 
269 
59 8 


71200 
301 
83 6 


78000 
330 
110 




78 


CU. FT. 
R. P M. 
B H. P. 


2t>J00 

88 

3 10 


37350 

124 

8 77 


45800 
153 
16 1 


52800 

176 

24 8 


59100 

197 

34 7 


64700 
215 
45 6 


70000 
233 
57.5 


74700 
248 
70 2 


8350O 
278 
98 


91600 
305 
129 




84 


CU. FT. 
R. P. H. 
B. H P 


308O0 

81 

3 61 


43400 
115 

10 2 


53200 
142 

18 7 


61600 

163 

28 9 


68700 

182 

40 4 


75200 
200 
53 


81200 
2I« 
66 8 


86800 
231 
81 7 


97100 
258 
114 


106400 
283 
1.S0 




90 


CU. FT. 
H. P. M. 
B. H. P. 


35250 

76 

4 14 


49S00 
107 
11 7 


61000 

i:{2 

21 5 


70500 
152 
33 1 


78800 

170 

46 2 


86400 

186 

60 7 


93300 
201 
76 7 


99600 
214 
93 6 


111200 
241 
131 


122000 
264 
172 



171 



Notes on Heating and "Ventilation 

driven at so slow a speed that it will not produce suf- 
ficient pressure to overcome resistance of the air flues. 
Choose the largest fan that, driven at sufficient speed 
to overcome the resistance of the air flue, will deliver 
a proper quantity of air for the purpose of ventilation. 
As an example : Suppose we wish to deliver to a build- 
ing 10,000 cubic feet of air per minute. Referring to 
the table, we see that we may use an 80-inch fan driven 
at 400 revolutions, in which case there would be re- 
quired 5 horsepower to drive the fan and the pressure 
produced would be .713 ounce or we might use a 
120-inch fan driven at 125 revolutions per minute, 
in which case the power required to drive the fan 
would be 2.9 horsepowers and the pressure produced 
would be .153. In the first case the fan is small and 
being driven at high speed the pressure produced is 
more than necessary to overcome the resistance required 
except when the flues are long and have a number of 
turns. In the case of the 120-inch fan, while the horse- 
power is much lower the pressure is insufficient to over- 
come the ordinary resistance. For ordinary purposes 
the pressure should be about .25-.50. Referring again 
to the table, we see that the 100-inch fan driven at 200 
revolutions per minute would require 3.15 horsepowers 
and produce a pressure of .274. This would be about 
the proper size of fan for most cases. The pressure 
required to overcome the resistance of the building de- 
pends very largely upon the capacity and design of the 
flues and the resistance of these flues is largely a mat- 
ter of judgment and experience. 

Heating Coils. — The determination of the proper 
quantity of heating coil to raise the air to a given tem- 

172 



Notes 



o n 



Heating and Ventilation 



Table XLVIII— Condensation 


and Heat Given Off by 








Heater Coils. 






d 




TEMPERATURE AIR ENTERING COIL 00-10° 


Velocity of Air 


Velocity of Air 


Velocity of Air 


Velocity 


' of Air 


<u 




1000 feet per 


1250 feet per 


1500 feet per 


1700 feet per 


CO 


(J 


minute. 


minute. 


mmute. 


minute. 


4j 


^- 


^_, 


^- 


*-> 


.^ 


j_) 


^_ 


o 




C o 


0)0 


== 2 


01 o 


c o 


<V'o 


c o 


0>o 


o 




aaw 


t;o 


.istS w 


^6 


.22 w 


^o 


.22 w 


^° . 


m 


(/] 


^OJ'S 


-u) bx) W 


1^ <u'^ 


-u be m 


1^. <d'^ 


-u be 50 


^ OJ'^ 


-M be w 




c 


w ^^ ^ 


03 C 5^ 


K^^ 


j3 c J> 


" ti c 


Oi c ^ 


w ^ == 


o3 c J; 


a 

6 


o 

CO 

d 

2; 


-a erf* 


<P > Jh 

C Ol 01 


i 2 s 

o t-.S 


ti— o> 

1^ > h 

0,05 be 

'^ ^ 


33 = S 
U 0) 


t-— > 01 
'V > ^ 

ao3 be 


c rt ^ 

rrj o" '-'' 

o t..5 
U 01 


> Jh 

a oi t« 


o. 


c^ 


a 


03 


a 


o3 


a 


03 


4 


1 


2.90 


39 


2.4 


35 


2.68 


32 


2.85 


31 


8 


2 


1.92 


74 


2.21 


65 


2.46 


60 


2.65 


55 


12 


3 


1.78 


94 


2.1 


82 


2.32 


77 


2.45 


73 


16 


4 


1.53 


114 


1.86 


98 


2.09 


93 


2.25 


88 


20 


5 


1.31 


130 


1.68 


115 


1.88 


108 


2.10 


103 


24 


6 


1.20 


143 


1.54 


128 


1.77 


122 


1.92 


117 


28 


7 


1.10 


152 


1.45 


140 


1.70 


134 


1.85 


129 


32 


8 


1.05 




1.40 


148 


1.65 


140 


1.77 


133 








TEMPE 


RATURE AIR E 


NTERING con 


. 400-50° 




Velocity 


' of Air 


Velocity of Air 


Velocity of Air 


Velocity 


' of Air 




o 


1000 fe 


et per 


l<i50 feet per 


1500 feet per 


1700 fe 


et per 


.2 




min 


ate. 


minute. 


mmute. 


mmi 


Lite. 


,(_, 


^^ 


-•-> 


r_ 


■i-i 




•«-> 


>-^ 


o 




c o 


ajo ■ 


c o 


0) o 


C o 


^1^ 


c o 


01 o 


u 




o o ■ 


^ § 


o o • 


^ o 


o o • 


'^ S 


o o • 


u 3 






.X «1H w 


p "-^ . 


.S t»-( 03 


13 ^ . 




3 <^ . 




p ^ . 


lU 


o 


?!" = 


+j bi3 M 
ct C <l^ 


i^i'S 


-!-> be w 
rt c 3^ 


1?; = 


rt 0) 3^ 


^2^'S 


-u he w 
rt c 0) 


a 

o 

6 
2 


CO 

d 


o t-.5 
p. 


<u > ^ 
ftoJ be 

^•3 


c S o 
<i> ^ 2 

o U.5 
a 


fcH-H 0) 

> !-, 

art oc 

03 


O 01 
a 


t^ ;-, <U 
"^ 1^ b, 

Eh t- 

a 


^Sa 

o ;..5 
^a 


ari be 

C 0) 01 


8 


2 


1.75 


91 


2.07 


84 


2.37 


80 


2.52 


78 


12 


3 


1.50 


107 


1.80 


100 


2.06 


95 


2.23 


93 


16 


4 


1.41 


119 


1.65 


112 


1.89 


107 


2.02 


105 


20 


5 


1.37 


133 


1.60 


125 


1.80 


121 


1.90 


119 


24 


6 


132 


143 


1.50 


137 


1.67 


135 


1.77 


133 


28 


7 


1.26 


150 


1.40 


145 


1.56 


142 


1.64 


140 


32 


8 


1.14 


158 


1.30 


252 


1.48 


148 


1.52 


147 



173 



Notes 



on Heating and Ventilation 



perature will depend primarily upon the amount of heat 
given off per square foot of heater coil. 

Table XLVIII is obtained from the results of experi- 
ments made by the American Blower Company, of De- 
troit, and shows the condensation and heat given off by 
ordinary pipe heater coils under different conditions. 
Knowing the heat given off by the coil per square foot, 
under given conditions, the number of square feet of 
coil surface necessary may be obtained in the following 



t'^^^'a 




Fig. 62. 

manner: Multiply the air to be passed per hour by the 
difference between the temperature of the outside air 
and the temperature of the air after passing through 
the coil. Multiply this product by .2375. Divide the 
result obtained by 13.3, multiplied by the condensation 
per square foot of surface per hour, multiplied by 966. 
Let C = condensation per square foot of coil ; V = vol- 
ume of air in cubic feet passing per hour ; F = square 
feet heating surface coil should contain ; t = tempera- 
ture outside air : V = temperature of air after passing- 
coil ; then 

.2375V(t'— t) 
F = 

13.3 X 966 C 

174 



Notes 



o n 



Heating and Ventilation 



After determining the number of square feet of sur- 
face in the heater the heater must be so designed as to 
allow sufficient air area for the passage of air through 
the heater coils. The coils as ordinarily arranged are 
shown in Fig. 62. Sufficient area should be allowed in 
these coils for the velocity of air passing. This should 
not exceed 1,200 feet per minute, except where coils are 




Fig. 63. 

very large. Tempering coils should not be less than 12 
pipes deep. If the tempering coils are made very shallow 
the condensation in the coil is so rapid that in cold 
weather they will hammer. 

The heater coil consists of a cast iron base into which 
is screwed 1-inch steam pipes jointed at the top by 
nipples and elbows. The cast iron base for each section 
is provided with a steam inlet and drip, both connected 
to the cast iron heater base. Most bases are constructed 

175 



Notes 



o n 



Heating and Ventilation 



for four rows of pipes. Table XLIX gives the principal 
dimensions of the American Blower Company's heaters 
with the size of fan regularly used. 

Cast Iron Heaters. — Within the last few years cast 
iron indirect radiators suitable for use with fans have 
been placed on the market. Figure 63 shows a group of 
ten of these sections. They are easier to handle in erec- 
tion and less liable to rust. The standard sizes on the 
market are 41 and 60^ inches in length; both sizes are 
9% inches deep and each section takes up a width of 
5 inches. The 60-inch section contains 17 square feet 
per section and the 40-inch section 11^ square feet. 
The table sections are tapped 2^/2 inches and may 







TABLE 


1 XLIX.- 


-HEATER 


DIMENSIOTSrS. 




Lineal feet 








Net air 


Size of fan 


capacity 


of 


1 


r^onnections. 


space in 


Regular 


•Steel 


1-ineh pipe. 


Steam. 


Drip. 


Bleeder. 


sq. ft. 


Disc. 


Plate. 


200 




o . " 


1 " 


%" 


5.4 


30 


80 


300 




2- " 


1 " 


%" 


7.6 


36 


90 


400 




2 " 


IVa" 


%" 


10.7 


42 


100 


525 




2 " 


1%" 


1 " 


14.3 


48 


110 


650 




2 " 


11/2" 


1 " 


17.7 


54 


120 


825 




2W 


11/2" 


1 " 


22.2 


60 


140 


1,175 




2%" 


iy2" 


1 " 


31. 


72 


160 


1,525 




3 " 


" 


1%" 


40. 


84 


180 


2,025 




3 " 


2 " 


ly*" 


52.5 


96 


200 



be bushed to the proper size, depending on the 
number of sections composing the radiator. Fig. 64 
shows a curve of the steam condensation for these ra- 
diators with varying depth of coil and different veloci- 
ties of air. Figure 65 shows the temperature to which 
the air would be heated in passing through these coils 
with varying depth of coil and different velocities of 
air. The last two cuts are from the results given by 
the American Radiator Co. 

176 



Notes 



o n 



Heating and Ventilation 



Ventilating Ducts. — The success of the fan system 
depends very lai\e:ely upon the design of the flues. The 

Condensation Chart 



Incoming air, o" Fahrenheit. Steam pressure, 5 pounds 



105 
1.10 
115 
1 20 
1 25 
1 30 
1 35 
1 40 
1 45 
1 50 
1 55 
1 60 
1 65 
1 70 
1 75 
1 80 
1 85 
1 90 

1 95 

2 00 
2 05 



U. 2 



W) 



(J 













' 






' 




























\ 














































\ 


k 












































\ 


V 






































\ 






\ 


s. 






































\ 


\ 




V 


k. 






































\ 


s. 






\ 
































\ 






V 


s 






\ 
































\ 








\ 






\ 
































s 


s 






\ 






\ 


























\ 






V 


N, 






\ 






\ 


























\ 






V 


N, 






\ 






\ 


s 
























\ 


s. 






\ 






\ 






V 


s. 














■■ 




\ 






V 


s. 






\^ 






\ 


s 




V 


^'l 


► 


. 














\ 






N 


\ 






\ 






S 


\, 






^^ 


ft 
















s 


s 






\ 






\ 






\ 


s. 






\ 












\ 






s 


s. 






N 






\ 


s 






^v 


V 




N 












\ 


V 






\, 






\ 






N 


s. 






^ 


'Pm. 




'S 


\ 










\ 


s^ 






\ 






\ 






V 


N. 






% 






s 


s 










s 


s. 






\ 






\ 


V 




N 


^ 






\ 






V 


s. 












\i 






\ 






\ 


s. 






^J 


'0 




\ 


\ 




> 














\ 






\ 






V 


N, 






% 






\ 


s 


















N 






\ 


s 






^^ 


f- 




\ 






\ 


N. 


















\ 






\ 


s 






^ 


'0. 




\ 


s 
























\ 






s 


N, 






^ 






s 


s 
























\ 


s 




v 


<;^ 


1- 




\ 






\ 


s. 
























S 


s. 






^ 


if) 




\ 


s 






























V 


N 






^ 






s 


s. 
































^ 


s 




\ 






V 


S, 
































^ 


?.* 




N 


s 






































^ 






V 


s. 






































\ 


s 




V 


N 






































s 


s. 












































V 


\ 
























1 






















::^ 



500 600 700 -800 900 1000 1100 1200 1300 
Velocity of Air Through Heater in Feet per 

Fig. 64. 



1024 

1072 
1121 
1170 
1219 
1267 
1316 
1365 
1414 
1462 
1511 
1560 
1608 
1657 
1706 
1755 
1804 
1852 
1901 
1950 
1999 
2047 
20% 
2145 
2194 
2242 
2291 
2340 
2389 
2437 
2486 
2535 
2584 
2632 
2681 
2730 



C/3 



X 



Cu 



1400 1500 
Minute 



best form of flue is round, the next best form is square, 
or, if rectangular, is nearly square as po<;sible. All 

177 



Notes 



o n 



Heating and Ventilation 



turns and branches should be made with easy curves. 
The size of the flues is ordinarily determined by the 
velocity of the air passing in the flues. In main ducts 
of large size a velocity as high as 1,500 feet per minute 
may be used. In the branch main- or small main ducts 

Temperature Chart 

Initial air temi>erature, o° Fahrenheit. Steam pressure, 5 pounds 



u^- 














= 


= 






= 






= 


= 










= 




= 


210.° 














= 






:=: 


= 








200.° 












= 


= 






= 






= 


= 










p 




= 


190.° 
180° 
170° 
160° 
150° 














^ 


^ 






^ 






^ 


^ 










= 




— 












^ 


1 


1 






^ 






1 


%_ 










1 






140° 
130° 
120° 
110° 
100° 
90° 






^ 


:s: 




1 


i 


- 


= 






^ 


F=i 






^^ir 




= 












S 


kH 




1 


^ 


=•— 1 


=si 


1 






1 




=s 




frr 


^ 
^ 

^ 


§ 




= 


80.° 
70° 
60.° 
50.° 
40.° 
30.° 
20° 














1 


1 


Y 


^ 


1 






1 


1 


^ 


m 

^ 


aS 


ITOj 






— 


10° 

0° 














= 


= 






= 






^ 


1 










^ 







500. 600 700 800. 900. 1000. 1100. 1200 1300. 1400. 1500. 

Velocity of Air Through Heater in Feet per Minute. 
Fig. 65. 

the velocity should not exceed 800 to 1,000 feet. In 
flues leading to the individual rooms the velocity should 
be from 600 to 800 feet per minute, depending upon 
their size. Where the ducts are of small size this ve- 
locity is often reduced to 400 feet per minute. The 

178 



Notes on Heating and Ventilation 

velocity at the registers should not exceed 300 feet per 
minute except in very large registers so located that the 
current of air entering the room will not strike the occu- 
pants of the room, then the velocity may be 500 feet 
per minute. In all ordinary buildings, if these propor- 
tions of air velocities are used the resistance of the sys- 
tem will be from .3 to .6 of an ounce pressure. The 
loss of pressure in a piping system of square or round 
pipe may be determined from the following expression 
used by the U. S. Navy Department : 

1 
H, = 4f — Vi^ 
d 
. Where H is the loss of pressure due to friction meas- 
ured in head of air in feet, f is the coefficient of fric- 
tion, 1 and d are length and diameter of pipe, both in 
feet or both in inches, and V^ is the velocity of flow 
through the pipe in feet per second. If V^ is changed 
to V, or velocity in feet per minute, and f given its 
proper value, which for good piping is .00008, then 

1 V2 

H, = 

d 11,250,000 

1 

If V = 2,000, Hf = .3556 — 

d 

1 
If V = 1,000, H, = .0889 — 

d 

For rectangular pipe of short side h and long side nh 
the formula becomes : 

1 + n 1 V^ 

H, = 

n h 2,250,000 

179 



Notes on Heating and Ventilation 

Where 1 = length of pipe and V is velocity of air 
through it in feet per minute. If a standard pressure be 
assumed of 5 pounds per square foot, which corresponds 
to a head of air of 84.25 ft., then for each foot of head 
lost there will be a loss in delivery of .6 or 1 per cent. 
For example, suppose 364 feet per minute are required 
at a given outlet, where the total head is 69.67, a loss of 
15 feet. The corresponding loss of delivery would be 
9 per cent and the rated capacity of the pipe to delivery 
of this air should be 364/91 = 400 cubic feet per minute. 
In determining the length of a pipe a 90° elbow is 
equal to 5 diameters of pipe provided the radius to the 
center of the pipe is not less than 1^ diameters. A 
smaller radius than this should not be used, as it in- 
creases the resistance very rapidly. Where branches 
leave the main ducts it is a common practice to place 
a deflecting damper at the bend of the branch. This is 
merely a piece of galvanized iron attached to the point 
of the branch, which may be adjusted and fastened so 
that each branch will take its proper supply of air. 
Dampers controlled by the attendants in the building 
should be as few as possible. The reductions in the size 
of a flue should be made gradually. The angle of the 
reduction should not exceed a taper of 1^" per foot. 
No round pipes less than 6 inches in diameter are used, 
and if rectangular, less than 6x8. A common arrange- 
ment of ducts is to let them radiate from the fan in the 
form of a tree, with trunk and branches. Another very 
satisfactory method of distribution is to force all the 
air from the fan into a large duct or chamber in which 
the air has a very low velocity. 

180 



Notes 



o n 



Heating and Ventilation 



The rooms take their air from this chamber by means 
of vertical flues controlled by proper dampers. These 
large chambers are called Plenum chambers. A g:ood 

TABLE L.— PRESSURE LOSSES. 

Air. — Loss of Pressure in Ounces per S'quare Inch per 100 Feet of 
of Pipe of Varying Velocities and Varying Diameters of Pipes. 



Velocity of Aii 
Feet per 
Minute. 



600 
1,200 
1,800 
2,400 
»,000 
8,600 
4,200 
4.800 
6,000 



Velocity of Air 
Keet per 
Minute. 



600 
1,200 
1,800 
2,400 
8,600 
4,200 
4,800 
6.000 









DIAMETER OK 


PIPE IN INCHES. 






Velocicy ol Aft 
Feet per 
Minute. 


1 


2 


3 


4 


6 1 6 


7 


8 




Loss OF PrESS(.>KE IK OvsCcs 


600 
1,200 
1,800 
2,400 
8.000 
8,600 
4,200 


.400 
1.600 
8.600 
6.400 
10.000 
14/400 


.200 
.800 
1.800 
8.200 
5.000 
7.200 
9.800 
12.800 
20.000 


133 
.533 
1.200 
2.133 
8.333 
4.800 
6.5.')3 
8.533 
13.333 


.100 

.400 

JWO 

1.600 

2.500 

8.600 

4.900 

6.400 

10.000 


.080 
.820 
.720 
1.280 
2.000 
2.880 
3.<*20 
5120 
8.000 


.067 
.267 
.600 
1.067 
1.667 
2.400 
3.267 
4.267 
6.667 


.057 

.22« 

.514 

.914 

1.429 

2.057 

2.800 

8.6.57 

5.714 


.050 

.200 

.450 

.800 

1.250 

1.800 

2.450 


4,800 
6,000 




8200 
&.000 







DIAMETER OF PIPE IN INCHES 



11 



18 



14 



16 



18 



Loss OF Pressure i.n Ounces. 



.044 


.040 


.036 


.033 


.029 


.028 


.022 


178 


.160 


.145 


133 


.114 


.100 


.089 


400 


.360 


.327 


.800 


.257 


.225 


200 


.711 


.640 


.582 


.533 


.457 


.400 


856 


1 111 

1.600 


1.000 


.909 
1.809 


.833 
1.200 




■".'900 




1.029 


.800 


2.178 


1.960 


1.782 


1.633 


1.400 


1.225 


1.089 


2.844 


2.560 


2.327 


2.133 


1.829 


1.600 


1.422 


4 444 


4.000 


3.636 


8.333 


2.857 


2.500 


2.222 



DIA.METER OF PIPE IN INCHES. 



28 



24 



28 



32 



36 



40 



44 



Loss OF Pre.v<i'Re in Ounces. 



.018 


.017 


.014 


.012 


Oil 


.010 


.009 


.073 


.067 


.057 


.050 


.044 


.040 


.036 


.164 


.1.56 


.129 


.112 


.100 


.090 


.082 


.291 


.267 


.289 


.200 


.178 


.160 


.145 


.6.55 


.600 


.514 


.4.50 


.400 


.360 


.827 


.891 


.817 


.700 


.612 


,.544 


.490 


.445 


1.164 


1.067 


.914 


.800 


.71) 


.640 


.582 


1.818 


1.667 


1.429 


1.250 


I.IU 


1.000 


.909 



20 



.020 
OSD 

m 

.820 



.■no 

.980 
1.280 
2.000 



48 



.008 
.0:13 
.075 
.133 
.300 
.406 
..583 
.833 



example of this is shown in the construction of the new 
Engineering building, University of Michigan. In this 
building the corridor on the ground floor has a false 



181 



Notes 



o n 



Heating and Ventilation 



ceiling about 3 feet below the second story floor. This 
leaves a space 3 feet high by 12 feet wide extending 
through the entire building. Into this space two separate 
fans deliver their air. The space acts as a Plenum 
chamber and the individual flues leaving the rooms take 
their air from this Plenum chamber through volume 
dampers which may be set and fastened after the proper 
position has once been determined. 

Table L shows the loss of pressure per 100 feet of 
pipe for varying velocities and varying diameters of 
pipes. This table is quite liberal and allows for two 
ordinary 90° bends per 100 feet. 

Air Mixing Systems. — Where the building is heated 
entirely by a fan system it is necessary to devise some 
arrangement by which the room may be furnished with 




Fig. 66. 



hot air or tempered air. In case the room becomes too 
warm, to close off the hot air register would do away 
entirely with ventilation and it is necessary to provide 
some means of introducing tempered air. The method 
usually is shown in Fig. 62. Where each room is con- 
nected both to the warm air chamber and to the cold air 
passage, the dampers being connected so that when the 
warm air is turned off cold air is introduced into the 
room, or vice versa. In this case the mixing damper is 

182 



Notes 



o n 



Heating and Ventilation 



located near the fan and preferably controlled automat- 
ically. Another system shown in Fig. Q6 has entirely 
separate cold and hot air flues which are led to the base 

TABLE LI.— DISC FAN EFFICIENCY. 

Dies Ventilating Fan — Capacity, Speeds and Horse Powers (Amer- 
ican Blower Co.) 



Air V«ioc- 
iTv IN Ft. 

»R MiN. 


Size 
Fan 


18 


21 


24 


30 


36 


42 


48 


54 


60 


72 


84 


96 


106 


120 


600 


Fret 


Cu. Ft. 

R. P. M. 

HP. 


1060 
.016 


.o?a 


1880 
245 
.028 


2940 
196 
04S 


4230 

165 

. 064 


5772 
140 
087 


7536 
"3 


9540 

'<5 


11770 

98 

■'77 


16960 

82 
253 


23090 

70 
■345 


30156 

■450 


38160 
55 

573 


47160 
50 

706 




Heater 


R. P. M 
.H. P. 


530 
053 


453 
072 


396 
094 


3'7 
•.'47 


267 


227 

.288 


'97 

377 


«78 
.477 


158 
590 


849 


"3 
I 15 


100 
• 5' 


89 
1.91 


81 
'35 


700 


Frit 


Cu. Ft. 

R. P. M. 

H. P. 


1235 


1680 
328 
03S' 


2»00 
980 
■045 


3400 
«30 

.070 


4940 

190 


6730 
.64 
■36 


8800 
'45 
..78 


1II20 

"7 

.227 


J3750 

.279 


19760 

96 

■ 402 


26950 
■ 548 


35016 

72 

.740 


44500 
■ 62 
.905 


5S0OO 

58 

1.11 




Heater 


R. P. M. 
H. P. 


600 

.071 


530 

.096 


.ij6 


.196 


32' 
.283 


266 
•384 


234 

503 


206 

.636 


J 78 
.786 


'58 
• '3 


'32 
•54 


116 
2.10 


■ 00 
2.52 


92 
3 '4 


800 


Free 


Cu. Ft. 

R. P. M. 

H. P. 


1410 
.036 


19*0 

"1 

048 


2510 
326 
.068 


3820 

202 
098 


5650 
218 
.'42 


7700 
187 
192 


10300 
J 64 
.251 


12710 
'45 
■3'7 


15710 
'3' 
392 


22600 
.562 


30400 

94 

.766 


40150 
1 » 


50900 

73 

1 27 


62800 

66 

'57 




Heater 


R. P. M. 
H. P. 


705 
.106 


604 
'49 


.189 


424 
»94 


.426 


302 


265 
•756 


'34 
957 


I 18 


178 
' 7" 


"52 
2.32 


'34 

3 20 


Its 

383 


107 
4 73 


900 


Free 


Cu. Ft 

R. P. M. 

HP. 


■584 
490 
•048 


2160 

06s 


2826 
j68 
.085 


132 


6354 
246 
.190 


8650 

.^8 


I1304 
184 
•338 


143.0 
164 

.42S 


17667 
146 
53° 


'5443 


34642 
106 
I 04 


45234 
« 35 


57250 

82 

1.72 


70650 

74 

2 12 




Heater 


R.P. M. 
HP. 


79» 
M3 


770 

■95 


595 
254 


46- 

397 


398 

572 


3J° 

.780 


298 


265 
1 29 


236 
• 59 


»99 
»j»9 


'73 

3 12 


150 
4 07 


'3' 
5 '5 


119 

6.36 


1000 


Free 


Cu. Ft. 

R. P. M. 

HP. 


1770 
54 5 
057 


J4CX) 
470 
080 


3140 
406 
.104 


4900 
328 
'42 


7060 
275 
233 


96.0 
234 
3'7 


12560 
205 
4'3 


159CO 

iSi 
.520 


19630 
166 

647 


28270 
136 
933 


38480 
110 
1 27 


50265 


63603 

9' 

2.09 


78540 
2.56 




Heater 


R.P. M. 

rt.p. 


883 
.204 


760 
.J76 


657 
^6, 


530 

.565 


814 


378 


332 
' 45 


.11 


2C8 
2.26 


3 26 


.94 

4 44 


'67 
5 77 


,'47 
7 33 


'■3' 

9 OS 


1200 


,„. 


•Cir.Tt. 

R. P. M. 

HP. 


654 


j88o 
.138 


V3768- 


.5880 


8472 

330 

.405 


"54' 
280 
550 


15072 
245 
.7.6 


19100 
.910 


J3566 

>96 

in 


33900 


46.76 
140 
2.20 


60312 
-'85 


76300 
Vio 
363 


94240 

4^48 




Heater 


R. P. M. 
H. P. 


>o59 
.300 


9t» 

409 


,.788 
534 


636 
832 


534 


1.64 


.396 
2 14 


35' 
2 70 


322 

3 37 


264 
4 85 


6 60 


200 
8 63 


,'A 


..60 

''3 3 


1400 


Free 


Cu. Ft. 

R. P. M. 

HP. 


>47S 
767 
«33 


s 


4400 
570 
'3? 


6850 
460 
.,68 


9870 
38B 
530 


'3470 
327 
721 


17600 
286 
942 


22270 
254 
1.19 


27500 
230 
'55 


39600 
190 


53900 
289 


70300 

■44 

, 3 77 


'"tit 
4 77 


109500 
"5 

589 




Heater 


R. P. M. 
H. P. 


i»'3S 
■487 


to64 
.660 


.Ul 


742 
'35 


623 
'95 


2.64 


^^l 


*'2 
438 


376 
540 


^.88 


10. 6 


»34 
«J8 


205 
'f 5 


21.6 


1600 


Free 


Cu. Ft. 

R. P. M. 

HP. 


2830 
875 
■8S 


3850 
750 
25J 


5000 

656 
■ 330 


,8.0 
526 
•515 


II300 
438 
■ 742 


15400 
375 


20050 
33= 
'34 


25400 
298 
I 67 


3'40o 
264 
2 06 


45200 

220 
2 97 


61500 
168 
4 05 


80000 

16s 


101200 
146 

6.68 


125900 




Heaier 


R. P. M. 

H. P. 


1411 

735 


1J16 
1. 00 


1050 
'if 


848 
2 04 


712 

2 94 


603 
4 00 


537 
5 23 


468 

6 62 


8 17 


.^'8 


',l'i 


■ 268 
20 9 


234 
26 5 


210 

■3' 7 


1800 


Free 


Cu. Ft. 

R.P.M. 

H. P. 


»47 


4320 
840 
336 


5*3° 
73' 

440 


8850 
II? 


12700 
490 
99' 


17300 
420 
« 35 


22600 
1.76 


28600 
3*> 

2 22 


35200 
»94 


Siooo 
245 
397 


354 
23 


90200 
185 

7 0t 
302 

30.0 


114000 


141000 
148 
It.o 




Heater 


H. P. 


V588 
I OS 


.368 
■ 43 


■ 181 

• 87 


954 
« 93 


8^1 
4:<>3 


679 
S 75 


595 
7 so 


5»6 
9 50 


483 
11 7 


236 
47 




Free 


Cu. Ft. 

R. P. M. 

H. P. 


35SO 
1090 
33« 


4000 
456 


6280 
815 
■597 


9800 

655 

93' 


.4'2A 
545 

•34 


'9*4° 
470 
.83 




31800 
3«3 
3 02 


39260 
327 
3 73 


565. 

5 38 


76960 
'31 
7 3' 


100520 
206 

9 55 


127200 
182 


157100 


3000 


4'-o 

2 39 


164 
<4 9 




Heaier 


R. P. M. 
H. P. 


.764 
I 30 


1520 
• 77 


1312 
2 30 


ioft> 

360 


890 
5 '5 


755 
7 05 


664 
9 '5 


585 
117 


528 
'4 5 


440 
20 8 


2!^ 


336 
37 


292 
46 8 


262 
578 


2200 


Fret 


Cu Ft. 

R. P M. 

H P. 


3890 

4'4 


4300 

1050 
576 


6800 
900 

754 


loSoo 


15520 
600 

I 70 


21130 
S'5 

2 31 


97600 

450 

-3 <» 


35000 
400 
382 


•43200 
360 
4 72 


62200 
300 
6 79 


84700 
257 
9 25 


(10500 

228 


139800 
'5 3 


172500 

iJ!l 




Heater 


R P.M. 
HP, 


1940 
1 70 


1700 

a 30 


1460 
3 00 


1163 
4-70 


97' 
6 Bo 


830 

9 '5 


7»7 
. 12 I 


645 
'5 3 


.fj 


48s 
«70 


.4'5 
370 


r. 


61.0 


,84 

tl.O 



of vertical flues leading to the rooms, at which point 
there is introduced a mixing damper similar to the mix- 
ing damper shown in Fig. 62. 

183 



Notes on Heating and Ventilation 

Materials of Flues. — The flues for fan systems are 
ordinarily constructed of galvanized iron with double 
lap joints riveted or soldered. The ducts should be made 
as nearly as possible air-tight. The weight of material 
used for ducts depends upon the size of the duct. It 
ordinarily varies from No. 26 to No. 20 gauge. Large 
ducts are also made of sheet iron with close riveting. 
When ducts are made of sheet iron the ducts are painted 
and then asphalted. Where it is necessary to build ducts 
underground they are built of brick or cement. The ce- 
ment, if anything, is preferable to brick, as it does not 
absorb odors as easily and may be plastered to make a 
smooth job. Where possible it is desirable to build the 
ducts and flues into the building itself, making them of 
permanent material. Brick or cement ducts built into 
the building and so arranged that they may be examined 
and cleaned easily are the most satisfactory. Wood is 
always a bad material to use for ducts and should be 
avoided. Where it is used the ducts are lined with tin, 
owing to the fact that wood usually shrinks, leaving 
open joints. 

Vent ducts from closets should be carried out of the 
buildings separately from the other vent flues. Where 
these ducts are made of brick they should be lined with 
galvanized iron to prevent the odors from the closet be- 
ing absorbed by the brick. It is very desirable that 
closet vents should be collected at convenient points and 
then exhausted from the building by means of a fan. 
This prevents the odors from the toilet rooms being car- 
ried back into the building. 

Disc Fans. — Disc fans are used where the resistance 
to be overcome is very slight or in cases where the ducts 

184 



Notes on Heating and Ventilation 

are very large, with easy turns and of very short length. 
They are extensively used for exhausting the air from 
the vent flues and where the vent flues are short and 
large they give good satisfaction. The capacity, speed 
and horsepower of various sizes of disc fans is shown, 
in Table LI. 

Example. — As an example of the fan system consider 
an auditorium. The dimensions of the room are 40 feet 
9 inches by 79 feet G inches by 127 feet 9 inches. The 
volume of the room is 413,000 cubic feet. It has 203 
square feet of glass surface and 5,441 square feet of wall 
surface. The heat lost from the room, figuring in the 
same way as we have for previous examples, will be 
168,010 B. T. U.'s. The hall has a seating capacity of 
2,500 persons. Allowing 2,000 cubic feet of air per per- 
son, the necessary air to be admitted to the room will 
be 5,000,000 cubic feet of air per hour. This equals 383.- 
000 pounds. In order to heat the room with this quan- 
tity of air entering, it will be necessary to heat the air 
but 1.85 degrees so that the air admitted to the room 
for ventilating purposes will be far more than that nec- 
essary for heating purposes. It is best, then, to figure 
on admitting air only for purposes of ventilation. To 
heat this air from zero to 70° would require 383,000 X 
.2375X70=6,353,000 B. T. U.'s. Referring to Table 
XLV, we see that a heater coil 12 pipes deep will heat 
air having a velocity of 1,250 feet per minute to a tem- 
perature of 82°, which is probably about the proper 
assumption to make in this case. The coil will condense 
2.1 pounds of steam per square foot per hour. Each 
pound s:ives up about 970 heat units, so that each square 
foot of heater coil will give ofif about 2,000 B. T. U.'s 
per hour. Then the number of square feet of heater coil 
required would be 6,350,000-^2,000=3,175 square feet. 

185 



Notes on Heating and Ventilation 

The heater coils are usually made of 1-inch pipe and 
each square foot of surface is equivalent to about 3 feet 
of 1-inch heater pipe, hence there will be required 3,175 
X3 or 9,525 feet of 1-inch pipe in the heater coils. The 
air to be admitted to the hall is 5,000,000 cubic feet per 
hour or 83,300 cubic feet per minute. The usual velocity 
allowed for the air passing through the heater coil is 
1,200 feet per minute. This will require an air area in 
the heater coil of 83,000^1,200=69.5 square feet. The 
area in the various heater coils will be found in the 
blower company's catalogues and is also given in Table 
XLVIII. This will determine the size of the heater coil 
to be used. 

On account of the size of the hall and the amount of 
air introduced, it will be best to have two fans for deliv- 
ering air into the building. Each fan would then need 
a capacity of 41,650 cubic feet per minute. In order to 
overcome the resistance of the flues the pressure should 
be from .4 to .5 of an ounce at least. From the table 
of fan capacities we see that a 180-inch fan running at 
150 revolutions would require 19.6 horsepowers and pro- 
duce a pressure of .503 ounces and give the air required. 
Assuming the air to be delivered to the hall by four 
ducts, these ducts being large, it would be reasonable to 
allow a velocity of 1,000 feet per minute in the duct. 
Each duct would have to carry 20,800 cubic feet of air 
per minute; 20,800-^1,000=20.8 square feet in area. As 
the registers of these ducts will be large and situated 
well above the head line, it would be safe to allow a 
velocity of 400 feet per minute through the register. The 
area of each register, assuming that there are four en- 
tering the room, would be 26 square feet. The vent 
flues leaving the room should have an area about equal 
to the hot air flues. 

186 



CHAPTER Xil. 

A CENTRAL HEATING SYSTEM. 

Design and Location. — It is not intended in this 
chapter to discuss the design of heating systems, such 
as is used in the heating of a city, but systems that 
are in use for the heating of public institutions, or 
groups of buildings. The type of system to be used 
in a given installation depends very largely upon the 
location and. character of the building to be heated. 
No two systems, even though designed by the same 
engineer, will be the same, and the suggestions made 
in this chapter can be but general. 

Before starting the design of a general heating sys- 
tem it is first necessary to have a careful survey of 
the property. This survey should show the exact 
location of the buildings to be heated, the elevation 
of the basement and first floor, together with a gen- 
eral profile of the ground through which the tunnels 
or pipes are to be run. The profile of the ground will 
largely decide the proper location of the power house. 
The power house should be located as nearly as 
possible to the buildings to be heated or as near as 
possible to the largest steam load. It should be low 
enough, if the profile of the land will permit, so that 
the condensation of the return mains may be returned 
to the power house by gravity. If possible, it should 
be so located that the floor of the boiler room may 
be drained to the sewer. Considerable difficulty is usu- ■ 
ally experienced to carry away the water, which re- 
sults from the cleaning and blowing off of the boilers 

187 



Notes on Heating and Ventilation 

if no sewer connection can be made. The question of 
the soil, the location of the railroad siding, the water 
supply and the general appearance of the power house 
must also be taken into consideration. 

Boilers. — Before designing the power house the 
type and general form of boilers must be determined. 
If the power house is to work on a low pressure system 
with a pressure under 100 pounds, either fire or water 
tube boilers may be used. In general, for this service 
fire tube boilers are very satisfactory, as they have 
large water storage, repairs are easily made, and the 
boiler may be crowded considerably beyond its rating. 
The economy of water tube and fire tube boilers is prac- 
tically the same. 

The principal objection to fire tube boilers, except of 
the Scotch marine type, is the large space which it oc- 
cupies. If the power house is to be operated on high 
pressure, that is, over 100 or 125 pounds, then only 
water tube or Scotch marine boilers can be used. The 
size of the boiler must be determined by the amount 
of steam which is to be used by the radiation and other 
devices taking steam from the boilers. The steam used 
by the dififerent forms of radiation can be determined 
by reference to the radiator tables previously given, 
and to this must be added the steam used by auxiliaries, 
by the kitchen, the condensation in the ' main and all 
other devices using steam. After having once de- 
termined the quantity of steam the plant is expected 
to use, it is customary to assume that each 
square foot of heating surface in a boiler will 
evaporate about three pounds of water. This deter- 
mines the total 'imount of heating surface that the 

188 



Notes on Heating and Ventilation 

boilers should contain. The boiler units should be so 
selected that one boiler or one set of boilers will take 
care of the plant during the light load period of opera- 
tion, that two boilers or sets of boilers will take care of 
the average operating load. In addition to this there 
should be a boiler or set of boilers that will take care 
of the maximum conditions of load. There should al- 
ways be a sufficient number of boilers in the plant so that 
at least one boiler or set of boilers can be out of service 
for a considerable period of time for cleaning or re- 
pairing. In a central heating plant using the gravity 
return system, it is necessary that all boilers have their 
water line at the same level. 

Systems of Distribution. 

The general design of a piping system and its lo- 
cation will depend upon the system of distribution 
adopted. 

Gravity System. — If the gravity return system is 
used no main feed pump is necessary, the water re- 
turning by gravity to the boiler, as previously described. 
With this system any difference in pressure between 
that in the boiler and that at the extreme point in the 
piping system will result in a corresponding elevation 
of the water level in the return system at the extreme 
point — each one pound drop of pressure in the steam 
piping corresponds to an increase in the level of the 
water in the return piping of 2.30 feet. It is essential, 
then, that with a gravity return system the difference in 
pressure between the boiler and the extreme point of 
the piping system be comparatively small. 

The difference of pressure assumed will determine 

189 



Notes on Heating and Ventilation 

the size of the piping. In gravity systems it is usual 
to allow for the drop of pressure not over two pounds 
between the boiler and the extreme end of the system. 

In some cases the gravity return system has been 
used over quite an extended area, the most distant build- 
ing heated being as far as 2,500 feet from the boiler, and 
the system has given very good satisfaction. 

In a central heating plant using the gravity return 
system unless the steam mains are six to eight feet above 
the return it is necessary that the steam condensed in 
the mains be dripped separately from the main re- 
turns in the building and this drip pumped back to the 
boilers, preferably by a pump and receiver, or some 
other mechanical means, such as a return trap. This 
pump and receiver should be of sufficient size to take 
care of the steam condensed in the mains when the 
steam is being turned on and the condensation is ex- 
cessive. By returning the condensation of the mains 
separately, excessive hammering is avoided and the sys- 
tem can be started much more rapidly. Gravity return 
is used only where the boiler pressure does not exceed 
ten pounds. 

High Pressure System. — The high pressure steam 
is sometimes used for general heating purposes, but the 
pressure is reduced through a reducing valve before en- 
tering the radiators. It has some advantages. The 
pipes are smaller and circulation is very rapid in this 
system. It is not possible to use exhaust steam with a 
high pressure system. When pipe coil radiation is used 
it would be safe to carry a pressure up to 100 pounds on 
the radiators, but high. pressure in the radiators is not 
good practice. In determining the size of steam mains for 

190 



Notes on Heating and Ventilation 

such a system a loss of pressure as high as ten pounds 
would not be considered excessive. In the high pressure 
system each building usually sends its condensation back- 
to the return system through a trap so that the pres- 
sure on the return is only sHghtly above the atmosphere. 
This condensation returns to a surge tank, from which 
the feed pumps return it back to the boilers. The drip 
from the steam mains is dripped directly back into the 
return system. 

Low Pressure Pump Return System. — In a very 
large system where it is difficult to get enough differ- 
ence in elevation between steam and return mains, or 
where the drop in pressure exceeds two pounds, it is 
usual to install some form of pump return. One of the 
most common forms of pump return is to trap the re- 
turn condensation of each building into the return main, 
which carries the return back to a surge tank in the 
boiler room. From this surge tank the water is re- 
turned to the boiler by means of a pump. The drip 
from the steam main is trapped directly to the return 
main. The most objectionable feature of this system 
is the constant attendance and the repairs necessary to 
take care of the traps. 

Combination of Pov^er and Heating System. — In 
most cases the heating system is combined with some 
form of power system. This makes a very economical 
combination, as the exhaust from the power plant may 
be used in the heating system. Where the exhaust can 
be entirely utilized for from six to eight months of the 
year it is seldom profitable to use condensing engines. 

There are two general schemes used for combining 
a power and heating system. In the simplest form the 

191 



Notes 



o n 



Heating and Ventilation 



boilers are operated at a high pressure. The steam goes 
from the boilers to the engine, and after the steam 
leaves the engine it passes directly to the heating sys- 
tem. A by-pass pipe is carried from the high pressure 
steam main to the heating main and in this by-pass is 
located a reducing pressure valve. If for any reason 




Fig. 67. 

the engine does not supply sufficient steam to maintain 
pressure on the heating system, then the reducing valve 
opens and introduces live steam. The returns from 
the heating system are carried back to the boiler by 
means of a pump. 

Fig. 67 shows the general arrangement of systems 
of this kind with a by-pass for furnishing live steam to 
a heating system. This system depends in a measure 
for its success upon the action of the reducing pressure 
valve. 

The cross-section of a reducing pressure valve is 

192 



Notes 



o n 



Heating and Ventilation 



shown ill J^'ig'. (38. Such valves have been found to 
be quite reliable when well designed and well made. 
The principle cause for trouble is when the valve be- 
comes foul with dirt, in a system of this kind the en- 
gine exhaust is always provided with a back pressure 




Fig. 68. 

valve connected to the atmosphere. This valve is so 
arranged that if for any reason excessive pressure 
should accumulate in the heating system the valve would 
open and exhaust the steam into the atmosphere. The 
arrangement shown in Fig. 67 is most used in small 
plants and both the heat and the power can be taken 
from one boiler. In larger plants the heating boilers are 
operated on the low pressure and the power boilers on 
the high pressure system. In the high pressure system 
steam goes to the engine and pumps and is exhausted 
through an oil separator into the low pressure system. 
The pressure of the exhaust is determined by the pres- 
sure carried on the low pressure system. This system 
is particularly desirable where the heating load is con- 

193 



Notes on Heating and Ventilation 

siderably larger than the power load ; and where at 
times the engines are entirely shut down and only the 
low pressure system is operated. Fig. 69 shows a 
sketch of this arrangement. 




Fig. 69. 

Method of Carrying Pipes. — In carrying pipes from 
owe building to another it is always desirable, if possi- 
ble, to carry them underground. Carrying underground 
affords much better heat insulation, the pipes are more 
easily supported and are less apt to be disturbed. The 
simplest method of underground distribution and the 
cheapest is to enclose the pipes in a pine board case, as 
shown in Fig. 70. This arrangement, however, is not 
as desirable as a tunnel system, the heat insulation is 
not as satisfactory and the pipes are more difficult to 
get at for repairs. Its chief recommendation is that it 
is cheap. In most cases it should be used for work 
where the expense of a tunnel system would not be war- 
ranted. 



194 



Notes 



o n 



Heating 



and 



Ventilation 



A system quite largely used is to enclose pi[)es in 
pump logs, that is, hollow wooden pipes. These pipes 
are creosoted and filled with an asphah paint or some 
other means of preservation. They are often hned with 
tin or some other form of metal lining. The pipe is 
passed through the pump log and is usually covered with 
about one inch of some standard form of pipe cover- 




£'/ei/a/'^o/i 



Fig. 70. 



ing. This method of running the pipes furnishes quite 
satisfactory heat insulation. It is much more durable 
than the pine board duct, it is easier to install and easier 
to replace in case of repairs. It has, however, the dis- 
advantage of making the pipe quite inaccessible and in 
case of accident the removal of the entire system is 
necessary ; this in many places is very expensive. The 
builders of one of these pipe ducts stated that the loss 
in the pipes enclosed in this manner is from one-fourth 
of one per cent to six per cent per mile of pipe deliver- 
ing steam at its full capacity. The larger the pipe the 
smaller the proportional heat loss. Fig. 71 shows a 
cross section of a pipe log with covering. This pipe 
log construction is most used in central heating systems 
for building connections and where only one pipe is to 
be used in supplying the building. 

Where it is necessary to run a number of pipes the 
most desirable method is to run through tunnels made 

195 



Notes 



o n 



Heating and Ventilation 



of brick or cement. The size and form of tunnel used 
will depend upon the number of pipes to be carried, the 
character of the soil and the depth into the ground. 
Where tunnel systems have been installed the general 
experience has been that they more than paid for them- 
selves in a short time, as they entirely do away with 
the necessity of taking up the pipe and allow for repairs 



'77/7 /./nin^ 





£'/ev^/'/ 



^v^//on 



P/o. 



Fig. 71. 



and frequent inspection. Fig. 72 shows a small sized 
tunnel. This tunnel has been used for carrying pipes 
not over 8 inches in diameter. The tunnel is 3 feet 6 
inches wide, 4 feet 6 inches high. It is made of brick 
4 inches thick, with 1 inch of Portland cement outside. 
This cement is painted a thick coat of tar or asphalt to 
below the crown of the arch. Wherever the supports 
come the tunnel is ribbed with an 8-inch rib of brick 
16 inches wide. This rib is placed about every 10 feet. 
A tunnel of this kind has been in use for some time and 
has given good satisfaction. It is not desirable to use 
this sort of timnel for large pipe or where the tunnels 
are to be frequently inspected. 

For larger pipes the section shown in Fig. 73 is 
much more desirable. This tunnel is 5 feet by 6 feet 
inside dimensions. The tunnel is made of two 



196 



Notes 



o n 



Heating 



and 



Ventilation 



courses of brick or about 9 inches thick. It is plas- 
tered on the outside with 1 inch of cement and then 
tarred down to the crown of the arch. At the lowest 
point of the tunnel on each side is shown a 3-inch tile, 
which serves to carry away the drainage around the tun- 
nel. If possible, this 3-inch tile should be brought to 
some drain. In moist clay soils it is sometimes found 




Fig. 72. 

necessary to run a tile under the middle of the tunnel, 
connecting with the inside of the tunnel so that seepage 
through the tunnel walls may be carried off either to 
the sewer or to the ptimping plafit. In sand and in 
gravel soils this is not necessary, as almost no difficulty 

X97 



Notes on Heating and Ventilation 



would be experienced from leakage. Fig. 74 shows a 
tunnel made for carrying two large pipes. The tunnel 
is 5 feet 6 inches by 6 feet 6 inches and gives ample 




Fig. 73. 

passageway between the pipe supports for easy access 
at all times. 

The cost of tunnels depends upon the nature of the 
excavation and the price of materials. To give an ap- 
proximate idea of what tunnels cost, the tunnel shown in 

198 



Notes 



o n 



Heating and Ventilation 



Fig. 72 has been constructed, including excavation, back 
filling and all necessary material, for $7.00 per linear 
foot. The tunnel shown in Fig. 73 has been constructed 
for $8.00 per linear foot, and the tunnel shown in Fig. 70 
has been constructed for $9.00 per linear foot. 




'^ %■ ! 4 1 It , [ \j^ 

Fig. 74. 

Sizes of Pipes. — The size of the pipe necessary to 
carry a given quantity of steam is determined by the 
allowable loss of pressure that the system will permit. 
In a low pressure system this loss of pressure should 
not exceed 2 pounds. In a high pressure system it should 

X99 



Notes on Heating and Ventilation 

not exceed 10 pounds. The rule most commonly used 

is called Babcock's rule, and is as follows : 

Let W ^ weight of steam in pounds flowing per minute. 

w = the weight of a cubic foot of steam. 

p^ = pressure in pounds per square inch of steam enter- 
ing pipe. 

p, =: pressure in pounds per square inch of steam leav- 
ing the pipe. 

d = diameter in inches. 

L = length of pipe in foet. 

\v (Pi — P2) d, 

q f 

Then W = 87 l (1 H — ) 

d 

The best way of handling this expression is to 
assume different diameters of pipe and then try a 
number of standard pipe sizes. In this way deter- 
mine the pipe size which approximates most closely 
the weight of steam which it is desired to carry. 

In low pressure gravity return systems the return 
is usually taken as one-half the pipe size of the steam 
main up to 10 inches. Above 10 inches the size is 
taken as one-half the size of the steam main minus 
one size. As, for example, a 10-inch main w^ould 
require 5-inch return, a 14-inch would require a 6- 
inch return. The size of drip main for a given steam 
main depends entirely upon the length of the main. 
It should never be less than ^-inch and it is seldom 
necessary to make the pipe over 134-inch. A 134- 
inch drip main will take care of 2,000 feet of 12-inch 
pipe, providing the pipe is well covered with stand- 
ard covering. 

300 



Notes on Heating and Ventilation 

Hangers and Anchors. — When pipes are carried 
through tunnels it is necessary to provide a different 
form of hanger than in building work. In tunnel 
work the head room is so limited it is ordinarily im- 
possible to suspend pipes from above and they must 
have some form of roller hanger. Fig. 74 shows ball- 
bearing hangers for 12-inch pipe and roller hangers 
for the 6-inch pipe. Fig. 72 shows a very simple 
form of roller hanger. Fig. 73 also shows a form of 
ball-bearing hanger for 8-inch pipe and roller bearing 
for 4-inch pipe. The ball-bearing hangers shown in 
these figures have given very satisfactory results. 
They are expensive, but the expense is warranted. 
In tunnel work the clearance is so small that it is 
necessary to know exactly where the expansion is 
to be taken up. The only way to be certain of this is 
to anchor the pipe at the point desired. These an- 
chors are usually made of heavy cast iron with 
wrought iron straps enclosing the pipe. The hangers 
should be built into the tunnel or building walls and 
should pass entirely through the wall, projecting 4 
inches or more on the opposite side of the wall. The 
anchors should not be built into walls that are less 
than 12 inches thick, and preferably they should be 
16 inches thick. In putting in hangers and supports 
in tunnel work it is a very important thing to see 
that a clear space is left through the center of the 
tunnel which will give easy access to the tunnel. The 
easier the access and the more comfortable the tun- 
nel for passage, the more frequent will be the in- 
spections, and such inspections insure of the piping 
being kept in the best possible condition. 

301 



Notes 



o n 



Heating and Ventilation 



Air Valves. — Fig 75 shows an air valve adapted for 
use on large heating systems. The outlet of this air 
valve is three-quarters of an inch in diameter. It is 
particularly designed to take care of the air in the 




OUTLET J" PIPE 

Fig. 75. Air Valve for Use on Steam Mains. 

building and tunnel mains. The ordinary sized valve 
used in radiators is entirely insufficient to take care 
of large mains. Piping that is 4 inches and over 
should have the larger valves. With still larger pip- 
ing, 10 or 12 inches in diameter, where the mains are 
400 or 500 feet long, even this size is hardly sufficient 
to take care of the air unless a number of them are 
used. 

The valve shown in Fig. 7(1 is often used. This 
consists of a brass pipe ''A" four feet long, to which 
is screwed a 1^-inch angle valve. This pipe and 
angle valve are attached by a suitable elbow and 

303 



Notes on Heating and Ventilation 

nipple to the main from the point at which the air is 
to be removed. A yoke is fastened at elbow "B" 
and to this yoke two iron rods are attached. These 



,4i 






^ W**f."~-^' 




■^"^laeasesHe^J**" 



Fig. 76. — This Form of Air Valve is Often Used. 

iron rods are connected at the other end of the yoke 
"C." Yoke '*C" is attached to the valve stem of the 
angle valve. The threads are removed from the stem 



303 



Notes on Heating and Ventilation 

of the valve so that the valve will pass freely through 
the stuffing" box. By means of a lock nut on the valve 
stem the height of the valve disc above the seat may 
be adjusted. To start with, however, the brass rod 
"A" will be cold and the valve disc will be off the 
valve seat and air will be alowed to pass out pipe 
''D." As soon as steam comes the brass pipe "A" ex- 
pands, bringing the valve seat up against the disc and 
closing the valve so that no steam can escape. 




Fig. 77. Air Valve to Relieve a Fitting and Line of Pipe from Air. 

Another arrangement that may be used is shown in 
Fig. 77. At the point at which it is desired to re- 
move the air a 1-inch pipe is tapped into the fitting. 
Into this is tapped a 1-inch nipple, an elbow and a 
short piece of pipe, as shown. At the end of this 
short piece of pipe is attached a gate valve. At inter- 
vals along the inside of the pipe are attached large air 
valves, such as the one shown in Fig. 75. On start- 
ing up the system the gate valve is left wide open 
and remains open until steam begins to blow, then 
this gate valve is closed and the small air vajves take 

304 



Notes on Heating and Ventilation 

care of the accumulation of air that occurs from time 
*o time. 

Lack of proper air valves may cause serious acci- 
dents in the pipe system. In large pipes when steam 
is turned on it will circulate along the top of the 
pipe and the cold air remains at the bottom of the 
pipes ; the upper side of the pipe will then be hotter 
than the lower and hence will expand more than the 
under side. The tendency of the pipe is to assume a 
circular form, as shown in Fig. 78 by dotted lines. In 




Fig. 78. How Air Collects and Sometimes Breaks a Piping Sys- 
tem. How it Is Prevented. 

case of a very large pipe this has been known to 
wreck the piping system, breaking flanges and spring- 
ing the valve seats. Such a condition may be pre- 
vented by running the air pipes on the mains down to 
the bottom of the main, as shown in the figure, so 
that the air is removed from the bottom of the main 
instead of from the top of the main. In long piping 
systems it is very desirable that at intervals of not 
more than 100 feet air valves should be placed to 
remove the air from the bottom of the main. The 
size of these valves will depend upon the size of the 
main and they should be of ample capacity. It is 
not always necessary to use automatic valves. Auto- 

205 



Notes on Heating and Ventilation 

matic valves can be replaced by %-inch or ^^^-i^^^ch 
valves for this purpose. 

Air valves should be located at all high points on 
the return main, particularly at points where the 
return main rises, passes along the horizontal, and 
then drops down again. At such points air valves 
should be located at the top of the main. If this is 
not done the air will accumulate at these high points 
and prevent passage of water, sometimes almost as 
effectively as though the main were valved at these 
points. 

Surge tanks, traps and other devices where air may 
accumulate should be provided with air valves. In 
fact, when trouble is experienced in a steam pipe sys- 
tem one of the first things that the builder should 
assure himself of is that the air is being properly 
removed from all parts of the system. 

COMBINATION OF STEAM AND HOT WATER 

SYSTEM. 

There are a number of systems using a combina- 
tion of exhaust steam and hot water for use in con- 
nection with central heating systems. The exhaust 
from the engine is passed through an exhaust heater 
and the water heated in this heater is circulated 
through the heating system by means of a pump. In 
this way exhaust steam can be used for heating a large 
territory without producing any back pressure. This 
form of heating may be used in connection with a 
condensing engine. The water being circulated by a 
pump under pressure insures its actual circulation 
throughout the whole system and makes possible the 
use of relatively small mains for heating purposes, 

206 



Notes on Heating and Ventilation 

smaller than would be required for either low pres- 
sure steam or exhaust steam. In addition to the ex- 
haust steam heater there may he used either a hot 
water boiler or an auxiliary live steam heater, so that 
in case the exhaust is insufficient for heating the 
water, the water may be passed through this live 
steam heater, bringing it up to the proper tempera- 
ture. In some cases a Greene economizer has been 
used for furnishing additional heat, thereby making 
use of the waste from the boiler. 

Systems of this kind have been installed in a num- 
ber of cities and as high as one thousand houses 
heated from a central heating system. In these hot 
water circulating systems two general forms of pump 
are used, either a centrifugal pump driven by a mo- 
tor or engine, or a piston pump of the ordinary type. 
In most cases unless a high pressure is desired, a 
centrifugal pump is desirable. The central hot water 
heating system has one particularly desirable feature 
— the hot water leaving the system may be adjusted 
to correspond with the external temperature. The 
size of hot water mains is determined from the ve- 
locity of water circulating in the main. In small 
mains it should not exceed 2 feet per second ; in large 
mains it may be as high as 4 feet per second. 

Central heating by means of hot water is particu- 
larly adapted for residence districts, as the system 
can be installed with less expense per foot of main, 
making it possible to cover profitably an area having 
the houses scattered. Central heating with steam is 
particularly adapted for close business districts where 
steam is the usual form of heating and where the 
piping system will be relatively short for the load 
carried. 

207 



Notes on Heating and Ventilation 

In connection with the systems using pressure 
there must be used some form of expansion tank. 
Some of these systems use an open expansion tank, 
allowing the water in the return system to enter this 
open tank at practically atmospheric pressure, the 
suction of the circulating pump being connected to 
this open tank. Where this system is used a piston 
type of pump would probably be a desirable form. 
Where the centrifugal type of pump is used it would 
be desirable to use a closed tank. In this case the 
tank is partly filled with water and partly filled w^ith 
air. The expansion and compression of the air al- 
lows for the change in the volume of water due to 
changes of temperature conditions. In this case 'the 
pump will then only furnish the pressure necessary 
to overcome the resistance of the piping system. The 
air side of the expansion tank should be provided 
with an air pump, so that pressure may be maintained 
by means of an air pump on the air side of the sys- 
tem and the proper quantity of air carried in the tank 
at all times. 



208 



CHAPTER XIII. 

PIPING, COVERING AND OTHER 
APPLIANCES. 

Pipe Covering. — In all piping installation it is cus- 
tomary to cover the distributing pipes, except ra- 
diator connections. It is good practice to cover the 
risers passing through buildings, together with all 
steam and return mains. Where the water mains 
pass through rooms in which any drip from the pipes 
would be objectionable, such pipes are also covered 
to prevent the condensation of moisture on the out- 
side of pipes. In general the best form of non-con- 
ductor is dry air, which is so confined as to prevent 
circulation. In all successful forms of covering air 
is confined in the structure of the covering and the 
effectiveness of the covering depends largely upon 
the confining of this air. The effectiveness of differ- 
ent forms of covering was determined in a series of 
experiments made under the direction of Prof. M. E. 
Cooley, University of Michigan. Table LII shows the 
relative effectiveness of some of the different forms 
of covering. 

The results of these tests show that hair felt is the 
best non-conductor. It is not, however, suited for 
over 5 pounds pressure, as it chars and breaks down 
at higher pressure owing to the higher temperature; 
this is also true of the wool felts. In low pressure 
work at such temperatures as are ordinarily used, 
hair felt is found to be quite satisfactory. It is ex- 
pensive, but its expense is warranted in the saving 
from condensation in the piping. 

209 



Notes 



o n 



Heating and Ventilation 



TABLE LII. 
Relative Value of Different Pipe Coverings. 

Material of covering 
Moulding coverings. 

1. Asbestos 145 .319 1.23 136. .803 

2. Magnesia 119. .224 .94 166. .915 

S. Magnesia and asbestos. .125 .300 1.12 118. .879 

4. Asbestos and wool felt.. .190 .228 1.12 102. .910 

5. Wool felt 117 .234 1.16 110. .904 

6. Wool felt and iron with 

airspace 134 .269 ... 125. .828 

Sectional Coverings. 

7. Mineral wool 097 .193 .94 91. .952 

8. Asbestos sponge 105 .220 1.12 102. .920 

9. Asbestos felt 100 .217 1.35 94. .923 

10. Hair felt 080 .186 1.45 75. .960 

Non- Sectional Coverings. 

11. Two layers asbestos 

paper 388 .777 ... 364. .263 

12. Two layers asbestos 

paper, one inch hair 
felt and one thickness 
canvas 070 .150 ... 68. 1.000 

Table LIII shows the relative efifectiveness of differ- 
ent thicknesses of covering. Column 3 of this table 
shows the relative effectiveness of the various thick- 
nesses of covering compared with the bare pipe. From 
this table it is not a difficult matter to figure the 
amount of saving that may be made by using various 

TABLE LIII. 

Heat Transmission for Varying Thicknesses of Covering. 

Condensation Ratio of Conden- B. T. IT.'S 

Thickness of per sq. ft. per sation covered transmitted per 

covering. hour in pounds. to bare pipe. sq. ft. per hour, 

inches. ; ^] 

% .120 .281 167. 

% .117 .255 163. 

1 .107 .231 149. 
lU .099 .219 138. 
1% .087 .191 121. 

2 .078 .19 108. 

The covering used in obtaining the above results was a wool felt. 

210 



Notes on Heating and Ventilation 

thicknesses of covering. Knowing the amount of 
steam carried per year and the cost to produce 1,000 
pounds of steam, and having the results shown in 
this table, we can easily compute the financial saving 
to l^e made in the various thicknesses of covering. 
In doing this it is usually found that for 1)uilding 
work an incli covering is sufficiently heavy ; but for 
tunnel work and all work where the heat loss from 
the pipe is entirely lost and does not enter the build- 
ing it is economy to use covering 2 inches thick. 
Where superheated steam is used at high tempera- 
tures the covering is from '3 to 5 inches thick. Table 
LIV' shows the heat lost through a 1-inch wool cover- 
ing with various steam pressures. In covering a pip- 
ing system the fittings and valves should be covered 
the same thickness as the pipe. This also applies to 
flanges and steam traps. Where flanges and other 
parts which require removal are covered they should 
be covered so that the covering can be taken off 
easily. A satisfactory method of doing this is to 
form a covering composed of one layer of asbestos 
paper, 1 inch of hair felt and one thickness of 8- 
ounce duck. These are quilted together with cord so 
that the jacket is firmly held in one piece. This cov- 
ering is then fastened over the pipe to be covered 
by means of hooks and laces. 

TABLE LIV. 
Heat Transmission for Varying Pressures. 

Condensation Ratio of Conden- B. T. Tf^.'s Trans- 
Gauge per sq. sation of covered mission per 
pressure. ft. per liour. to bare pipe. sq. ft. per hour. 
5. .3 .108 .239 100. 
9.fi .111 .233 104. 
1.5.5 .126 .227 110. 
20.5 .134 .223 119. 

The advantage of covering may be shown from the 
following computation : 

211 



Notes on Heating and Ventilation 

Example. — In a given steam plant it was found 
that the heat lost from bare pipes per hour was 
3,355,000 B. t. u. In the particular plant in ques- 
tion the number of heat units required to make a 
pound of steam was 990, and this loss of heat would 
represent a condensation of 3,390 pounds of steam 
per hour. Assuming an evaporation of 9 pounds of 
steam per pound of coal this would be equivalent to 
376 pounds of coal per hour. If the plant were op- 
erated 365 days in the year and 20 hours a day, and 
the coal cost $3.25 per ton, the yearly loss would be 
$2,069. By covering the pipe 1 inch thick with hair 
felt the loss which would result from the bare pipe 
would be reduced to 15 per cent, which equals $314, 
making a saving of $1,755 by putting on covering. 
This amount capitalized at .10 per cent would repre- 
sent an investment of $17,550. In the particular case 
in question the actual cost of the covering was but 
$3,500. 

Air Valves. — In steam piping work it is very im- 
portant that the piping system be provided with suf- 
ficient number of properly located air valves. Pri- 
marily, air valves should be located at the points in 
the piping at which air accumulates in quantity. We 
are familiar with the fact that when a radiator is not 
provided with an air valve steam will not circulate 
into it and it does not become warm. This is also 
true of both steam mains and the return system. The 
writer has seen the entire return system of a building 
plugged with air on account of there being no air 
valve on a high point in the return main. 

For radiators an air valve similar to that shown 
in Fig. 79 is usually used. You will notice that this 

212 



Notes 



o n 



Heating and Ventilation 



air valve allows air entering from the connection to 
the radiator to pass directly to the top of the air valve 
body and out through a small hole or opening, which 
may be adjusted by means of a screw plug. If water 
enters the air valve, the water will rise in the valve 
body until the copper float, having a pin on its upper 
end, rises so as to close the exit from the air valve, 






Fig. 79. Type of Air Fig. 80. Air Valve Fig. 81. Air Valve 

Valves Commonly Used on Radiators Adapted to Hot 

Used in Radiators. In Connection with Water Work. 
Paul Valve. 

and no water is allowed to escape. When steam en- 
ters the air valve the expansion plug shown at thr 
center of the air valve expands, raising the copper 
float, again closing the outlet from the air valve. 

Fig. 80 shows an air valve which is used for radi- 
ators in connection with a system of air piping from 
the air valves. (1) is a cap screw screwed down on 
the valve with a lead washer, making a tight seat. 

(2) is a hollow screw upon which the expansion post 

(3) sets, closing the valve. The adjustment of the 
valve is done with screw (2), and this may be done 

213 



Notes on Heating and Ventilation 

without disturbing- the valve. (3) is a hollow part 
fastened at (5) and held in place by the union (6). 
This should never be disturbed. (4) is the nipple of 
the valve body, by which it is attached to the ra- 
diator. This is the union for attaching to the piping 
of the Paul system or other air piping system. (7) 
is a nut which forms the union for attaching this pip- 
ing. The operation of the valve is as follows : The 
air is drawn in from the radiator through nipple (4) 
into the valve between the adjusting screw (2) and 
the composition part (3) passing down through (3) 
into the pipe. When steam enters the composition 
part becomes heated and expands, thereby closing the 
opening between (3) and (2). When air again ac- 
cumulates and cools this composition part contracts, 
permitting air to be drawn through the tube. 

There are two typical forms of air valve, one clos- 
ing off the air by the action of the float, the other 
closing off the air by the action of heat expanding 
a plug. Fig. 79 shows a combination of these two 
principles, which prevents the throwing of water or 
the discharging of steam. 

Fig. 80 exemplifies the simple expansion operation. 
The valve shown in Fig. 80 would allow cold water 
to pass. 

Fig. 81 shows an air valve particularly adapted to 
hot water work. In this air valve the float principle 
alone is used. Air enters in through the connection 
to the radiator, as shown by the arrow in the cut, 
passes under the float and escapes through a small 
tube which reaches to a point near the top of the air 
valve. As soon as the water enters the float lifts, due 
to the air compressed by the water under the float, 

214 



Notes 



o n 



Heating and Ventilation 



Table LV. 

WROUGHT IRON AND STEEL STEAM, GAS AND WATER PIPE 

TABLE OF STANDARD DIMENSIONS 



Diameter 


Circum- 
ference 


Transverse 
Areas 


Length of 
Pipe per 
Sq. Ft. of 


Length of Pipe 
Containing 
One Cubic Foot 


Nominal Weight 
Per Foot 




11 


"re 

3 <u 
ox 


0) 

■i-> 

(Q 

S u 

<5q 


c 

u 

0) 

4-1 

X 


c 

u 
<u 

B 


c 

u 


2 


5 <u 
fee/) 




a; a; 

o o 

<u u 
x> c 


In. 


In. 


In. 


In. 


In. 


Sq. 
In. 


Sq. 
In. 


Ft. 


Ft. 


Ft. 


Lbs. 


% 


.405 


.27 


1.272 


.848 


.0573 


.0717 


9.44 


14.15 


2513. 


.241 


27 


H 


.54 


.364 


1.696 


1.144 


.1041 


.1249 


7.075 


10.49 


1S83.3 


.42 


18 


% 


.675 


.494 


2.121 


1.552 


.1917 


.1663 


5.657 


7.73 


751.2 


.559 


18 


H 


.84 


.623 


2.639 


1.957 


.3048 


.2492 


4.547 


6.13 


472.4 


.837 


14 


H 


1.05 


.824 


3.299 


2.589 


.5333 


.3327 


3.637 


4.635 


270. 


1.115 


14 


1 


1.315 


1.048 


4.131 


3.292 


.8626 


.4954 


2.904 


3.645 


166.9 


1.668 


111^ 


m 


1.66 


1.38 


5.215 


4.335 


1.496 


.668 


2.301 


2.768 


96.25 


2.244 


111^ 


m 


1.9 


1.611 


5.969 


5.061 


2.038 


.797 


2.01 


2.371 


70.66 


2.678 


1154 


2 


2.375 


2.067 


7.461 


6.494 


3.356 


1.074 


1.608 


1.848 


42.91 


3.609 


11^ 


2^ 


2.875 


2.468 


9.032 


7.753 


4.784 


1.708 


1.328 


1.547 


30,1 


5.739 


8 


3 


3.5 


3.067 


10.996 


9.636 


7.388 


2 243 


1.091 


1.245 


19.5 


7.536 


8 


m 


4. 


3.548 


12.566 


11.146 


9.887 


2.679 


.955 


1.077 


14.57 


9.001 


8 


4 


4.5 


4.026 


14.137 


12.648 


12.73 


3.174 


.849 


.949 


11.31 


10.665 


8 


4H 


5. 


4.508 


15 708 


14 162 


15.961 


3.674 


.764 


.848 


9.02 


12.49 


8 


5 


5.563 


5.045 


17.477 15.849 


19.99 4.316 


.687 


.757 


7.2 


14.502 


8 


6 


6.625 


6.065 


20 813 19.054 


28.888 


5.584 


.577 


.63 


4.98 


18.762 


8 


7 


7.625 


7.023 


23.955 22.063 


38.738 


6.926 


.501 


.544 


3.72 


23.271 


8 


8 


8.625 


7.982 


27.096 25.076 


50.04 


8.386 


.443 


.478 


2.88 


28.177 


8 


9 


9.625 


8.937 


30.238 28.076 


62.73 


10.03 


.397 


.427 


2.29 


33.701 


8 


10 


10.75 


10.019 


33.772 31.477 


78.839 


11.924 


.355 


.382 


1.82 


40.065 


8 


11 


11.75 


11. 


36. 914 1 34. 558 


95.033 


13.401 


.325 


.347 


1.51 


45.028 


8 


12 


12.75 


12. 


40.055 37.7 

1 


113.098 


14.579 


.299 


.319 


1.27 


48.985 


8 



Piping is often designated as "Merchant Pipe." This term is used to indi- 
cate soft steel pipe taken from stock. In sizes from % inch to 6 inch it is about 5-^. 
under the card weight and about 10^^ under card weight for sizes above 6 inch. 
Full weight pipe is made of stock that will produce pipe of full card weight. 



215 



Notes on Heating and Ventilation 

and the rubber valve held by the rim closes the open- 
ing through v^^hich the air escapes. The valve as 
shown here is made for connection to an air valve 
piping system. A similar valve is made without this 
connection. In the air valve shown for connection 
to a piping system there is a three-way plug cock in 
the air valve, Avhich allows of air and water being 
drawn directly to the air pipe system and of being en- 
tirely closed oflf. 

Pipe. — Piping for heating systems is made either 
of wrought iron or mild steel. An extra price must 
be paid for wrought iron pipe. The smaller sized 
pipes up to and including 1^4 inches are butt welded 
and are tested to 300 pounds pressure. Large sizes 
are lap welded and tested to 500 pounds pressure. 

Pipe is shipped in lengths of from 16 to 20 feet and 
is threaded at both ends, but a coupling is put on 
only at one end. 

The standard size pipes in use are given in ta- 
ble No. LV. 

Piping is often designated as ''Merchant Pipe." 
This term is used to indicate soft steel pipe taken 
from stock. In sizes from i/s-inch to 6-inch it is about 
5 per cent under the card weight and about 10 per 
cent under card weight for sizes above 6-inch. 

Full weight pipe is made of stock that will produce 
pipe of full card weight. 

Both steel and wrought iron piping is designated 
as wrought iron pipe. If wrought pipe is desired it 
should be called "strictly wrought iron pipe." 

Piping is made in three weights — standard pipe, 
the dimensions of which are given in Table 42 ; extra 

216 



Notes on Heating and Ventilation 

strong pipe, suitable for working pressures up to 2o() 
pounds ; double extra strong pipe, suitable for work- 
ing pressures up to 500 pounds. 

Fittings. — For heating work standard weight cast iron 
screwed fittings are used up to 6 or 8 inches in diameter. 
Above that it is usual to use flange fittings. 

When screwed fittings are used, flanges must be 
placed in the piping to provide for disconnecting in 
case of repairs. In screwing pipes into fittings the 
pipe grease should always be placed on the pipe 
threads so that the excess will not be left in the fit- 
tings. 

In describing a tee always give the dimensions of 
the "run" first and of the side outlet last. A bullhead 
tee is one in which the side outlet is larger than the 
outlets in the "run." 

It is better practice to use reducing elbows or re- 
ducing tees than to use standard tee or elbows and 
reduce them by means of bushings. 

Valves. — Valves 2 inches and under are made of 
all brass wnth removable discs. For radiators where 
the piping comes through the floor, angle valves are 
used. Where the piping comes over the floor ofifset 
or corner ofifset valves are used. Gate valves should 
be used in horizontal lines of piping which carry con- 
densation. Globe valves may be used in vertical pipes 
but not in horizontal pipes, as they dam up the water 
passing in the pipe. 

Where check valves are used they should be of the 
swinging check pattern. 

Valves above 2 inches are usually used with iron bod- 
ies and brass mountings and should have renewable disc 
seats. 

317 



CHAPTER XIV. 

AUXILIARY DEVICES FOR HEATING 
SYSTEM. 

A temperature regulator is an automatic device 
which will open and close the valve of the radiator 
so as to keep the room at a constant temperature. 
The temperature regulator in general consists of three 
parts. First, a thermostat which is so constructed 
that its parts will move with a change of temperature 
in the surrounding air and the motion of these parts 
will directly or indirectly open the dampers or valves 
which control the heat supply. Second, there must 
be some means of transmitting the motion from the 
parts of the thermostat to the valves or dampers con- 
trolling the heat supply. Third, some form of me- 
chanism for opening the valves or dampers. In most 
temperature regulating systems the thermostat mere- 
ly furnishes power enough to close or open an air 
valve or electric switch and thus start or stop the 
operation of the valves or dampers. 

The form most used at the present time uses com- 
pressed air to operate the valves and dampers. In 
the Johnson thermostat a small air valve is opened 
by the expansion of a curved strip composed of two 
materials having different rates of expansion. The 
bending of this strip due to change of temperature 
allows the air to escape and a small diaphragm to 
move back, thus opening a second valve allowing 
the air to come from the compressor or source of 
air supply and close the valve or damper on the 
radiator. When the room becomes cool the contrac- 

218 



Notes 



o n 



Heating and Ventilation 



tion of this strip closes the first small valve forcing 
out the diaphragm and closing off the compressed 
air supply to the valve or damper and releasing the 
air already in the valve or damper. Another form of 
thermostat extensively used is operated by means 
of a liquid confined in a thin metal vessel, the liquid 





Fig. 82. 

haxing a very high degree of expansion. As the 
liquid expands or contracts it controls the system of 
valves controlling the heat supply to the room. 

Temperature regulation is a desirable thing in all 
large heating systems, particularly for public Inijlcl- 

210 



Notes on Heating and Ventilation 

ings. The systems are quite expensive, but the ex- 
pense of construction is more than offset by the sav- 
ing in fuel bills. The saving in fuel bills in most cases 
is not less than 15 per cent and often as high as 20 per 
cent. In general the operation of these systems has been 
entirely satisfactory even after they have been in use 
some time without any attendance. The control of the 
temperature of the room should be regulated within 3 
degrees. With proper care these systems should con- 
trol the temperature of the room within 2 degrees. 
Temperature regulating apparatus is particularly de- 
sirable in school rooms ; this places the temperature 
of the room outside the control of the instructor and 
it is then free from his own personal ideas in the 
matter, thus adding much to the health and comfort 
of the occupants of the room. With the fan system it is 
difficult to get satisfactory operation without tempera- 
ture regulation. The application of temperature regula- 
tion to the fan system is shown in Fig. 83. 

Air Piping System. The discharge of air from the air 
valves and radiators often produces a very disagree- 
able odor and in addition it is very difficult to obtain 
an air valve which will not at times discharge a 
certain amount of steam or water. This difficulty 
may be overcome by using an air valve so designed 
that the discharge connection to the valve can be 
fastened to a piping system. The pipes and air valves 
are carried to the basement, collected into a larger 
pipe and discharged to a sewer or suitable vessel. 
A system of air piping is very desirable, particularly 
in large buildings, such as hotels and office buildings, 
where it saves materially in the attendance necessary 

230 



Notes on Heating and Ventilation 

to keep the plant in operation. It is also desirable 
in nice residences where any discharge of water or 
steam might injure the furnishings. In case it is 
desirable to install a vacuum system of heating this 
system could be connected directly to a vacuum pump 
insuring more rapid circulation in the radiation. 

Damper Regulators. It is always desirable in a 
steam or hot water heating plant, particularly steam, 
to Install some form of damper regulator on the 
boiler. In some heating plants it consists of an ordi- 
nary rubber diaphragm enclosed in a metal case. The 
stearn is allowed to come in contact with one side 
of the diaphragm, pushes a leyer attached to the other 
side of the diaphragm. This lever operates a damper 
controlling the air supply to the fire and sometimes 
also operates the check valve in the breeching. This 
is a very desirable arrangement, as it reduces the at- 
tendance necessary to keep the pressure in the boiler at 
the point desired. 

Humidity Regulation. — The humidity of the atmos- 
phere is a very important consideration in any heating 
system. When the air is very dry it is necessary for a 
room to have a mucli higher temperature in order that 
it may feel comfortable than when the air is moist. It 
is, therefore, important that we keep the humidity at a 
point as high as consistent witli satisfactory operation. 
Cold air contains proportionately less moisture than warm 
air, and therefore when cold air is heated and brought 
into a building it should be moistened in order to keep 
a proper per cent of humidity. The average humidity 
is al)out 70 per cent, in the arid regions humidity may 
be as low as 30 per cent. Humidity as low as 30 per 



Notes 



o n 



Heating and Ventilation 



cent produces irritation of the lungs and smarting of 
the eyes. In cold weather, if the humidity of the out- 
side air is 70 per cent and this air is heated and 
brought into the room without moistening, its humid- 




TO a* PA Si DIfyiPBR 



Fig. 83. 



ity may be reduced as low as 30 or 35 per cent, mak- 
ing the air as dry as in the most arid regions. This 
produces a serious effect upon the inhabitants and 
also the furniture of the room. The decrease of hu- 
midity due to the action of the heating system occurs 
particularly in the indirect heating system. There 
has been placed on the market what is called a humid- 



Notes 



o n 



Heating and Ventilation 



ostat. This is similar to a thermostat except that it 
is arranged so that as the moisture decreases in the 
room the liiimidostat opens up a series of steam or 
water jets in the air supply so that the air in ])assin<^ 




Fig. 83. 



through the steam or water jet takes up moisture. 
When the moisture gets to a certain percentage, deter- 
mined by the setting of the humidostat, the apparatus 
closes ofT automatically the steam or water jets. Such 
devices are particularly desirable in connection with 
school and hospital heating plants. 

Air Washers. — In the large cities the smoke and 
dust in the air makes it undesirable to introduce thjs 

933 



Notes 



o n 



Heating and Ventilation 



air directly into the room for ventilating purposes. A 
great many schemes have been tried to remove the 




Z2i 



Notes on Heating and Ventilation 

dust from the air. The earliest form was to use bur- 
lap screens through which the air passes. These 
screens work fairly well, but the finer dust will always 
be carried through them. A better plan is to pass the 
air through a sheet or series of sheets of water. After 
passing through these sheets of water the air is passed 
through an apparatus which removes the excess of 
water. Fig. 84 shows the general arrangement of an 
air washing system. As you will notice from the 
figure, the air first passes through a tempering coil 
which raises the temperature from 60 to 70 degrees, 
then passes through the sprays or sheets of water, 
then through the eliminator, where the excess of water 
is removed, and then it passes to the heating coils to 
be heated. The water used for washing the air is 
circulated over and over again by means of a small 
centrifugal pump driven by a motor. In some cases 
it is desirable that the air should be cooled. This may 
be done by placing cooling coils in the tank where the 
water collects after having washed the air, and reduc- 
ing the temperature of this water to the desired point 
or by washing with cold w^ater. The washing of the 
air with water also increases the humidity of the air. 
In a plant installed by the author the humidity of the 
air has been kept at a point not lower than 70 per cent 
by means of this washer. Air washing devices are 
very effective in removing dirt ; the amount of dirt 
removed in some cases is very large. 

Vacuum Heating Systems. 

In the systems of steam heating that have been de- 
scribed the steam has been used at a pressure higher 
than that of the atmosphere. Plants are now installed 

225 



Notes on Heating and Ventilation 

in which the pressure in the radiator may be atmos- 
pheric pressure or lower. The advantages of such a 
system are : 

First. Where exhaust steam is used the heating 
w^ill not increase the back pressure on the engines, 
but may reduce the back pressure. 

Second. The air can be completely removed from 
the coils and radiators. 

Third. There is perfect drainage through the re- 
turns, preventing all possibility of water hammer. 

There are two distinctly different types of vacuum 
heating systems, one in which the air is drawn from 
the radiator by means of an air pump through the air 
valve, as shown in Fig. 75, and the other in which the 
radiator is fitted with a special form of return valve 
and vacuum is maintained on the return system by 
means of a pump or aspirator. 

The best example of the first type is the Paul sys- 
tem. In this system the air valves are all connected 
to a system of air mains. These mains extend to an 
air ejector. This injector may be operated by either 
steam or water. The advantage of this system de- 
pends principally on the quick removal of the air from 
the piping and radiators. This action is often strong 
enough to produce a pressure in the radiator lower 
than atmospheric pressure. 

The vacuum system of heating in which the air is 
drawn from the air valves is particularly desirable in 
hospitals and school buildings, as it does away with 
the objectionable odor from the air valves. This vac- 
uum system of heating does away very largely with 
the attendance required by air valves. 

The best example of the second type of vacuum 

226 



Notes on Heating and Ventilation 

system is the Warren Webster. Fhis consists of an 
automatic outlet valve on each coil and radiator con- 
nected to a return system in which vacuum is main- 
tained by means of a pump. Iliese automatic valves 
are traps which allow the water of condensation to 
pass l)ut close as soon as the water is removed. 

One of the advantages of this system is that it 
permits of the quantity of steam entering the radiator 
to be regulated without any possibility of water ham- 
mer. 

This system always requires two pipe radiator con- 
nections, but has the advantage that the return piping 
may be made smaller than in a gravity return system. 

The vacuum system has other advantages. It also 
permits of the radiator being placed lower than the 
level of the boiler and the condensation is raised from 
the lower level by means of the vacuum in the system. 
Oftentimes this enables the engineer to overcome seri- 
ous difficulties in the design of the heating plant. 
These systems can be profitably installed in old plants 
where the steam mains are overtaxed, owing to fre- 
quent additions to the plant. By additions of the 
vacuum system these old mains can be made to carry 
a larger weight of steam, the vacuum system permit- 
ting a higher velocity of steam in the system without 
increasing the back pressure. 



227 



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